c#: Checking null for parameters.

Checking for non-generated code.
ref T8399

Reviewed-by: Felipe Magno de Almeida <felipe@expertisesolutions.com.br>
Differential Revision: https://phab.enlightenment.org/D10959

11 files changed, 71 insertions, 2 deletions

diff --git a/src/bindings/mono/eina_mono/eina_array.cs b/src/bindings/mono/eina_mono/eina_array.cs
index 37251be6cd..ba3809bf81 100644
--- a/src/bindings/mono/eina_mono/eina_array.cs
+++ b/src/bindings/mono/eina_mono/eina_array.cs
@@ -20,6 +20,7 @@ using System.Runtime.InteropServices;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Contracts;
 
 using static Eina.TraitFunctions;
 using static Eina.ArrayNativeFunctions;
@@ -468,6 +469,7 @@ public class Array<T> : IList<T>, IEnumerable<T>, IDisposable
     /// </summary>
     public bool Append(T[] values)
     {
+        Contract.Requires(values != null, nameof(values));
         foreach (T v in values)
         {
             if (!Push(v))
diff --git a/src/bindings/mono/eina_mono/eina_binbuf.cs b/src/bindings/mono/eina_mono/eina_binbuf.cs
index 24e93e8d9d..6cc79f9625 100644
--- a/src/bindings/mono/eina_mono/eina_binbuf.cs
+++ b/src/bindings/mono/eina_mono/eina_binbuf.cs
@@ -18,6 +18,7 @@
 using System;
 using System.Runtime.InteropServices;
 using System.ComponentModel;
+using System.Diagnostics.Contracts;
 
 namespace Eina
 {
@@ -214,6 +215,7 @@ public class Binbuf : IDisposable
     /// <returns>true on success, false if data could not be appended.</returns>
     public bool Append(byte[] str)
     {
+        Contract.Requires(str != null, nameof(str));
         return 0 != eina_binbuf_append_length(Handle, str, (UIntPtr)(str.Length));
     }
 
@@ -238,6 +240,7 @@ public class Binbuf : IDisposable
     /// <returns>true on success, false if data could not be appended.</returns>
     public bool Append(Binbuf bb)
     {
+        Contract.Requires(bb != null, nameof(bb));
         return 0 != eina_binbuf_append_buffer(Handle, bb.Handle);
     }
 
@@ -273,6 +276,7 @@ public class Binbuf : IDisposable
     /// <returns>true on success, false if data could not be appended.</returns>
     public bool Insert(byte[] str, uint pos)
     {
+        Contract.Requires(str != null, nameof(str));
         return 0 != eina_binbuf_insert_length(Handle, str, (UIntPtr)(str.Length), (UIntPtr)pos);
     }
 
diff --git a/src/bindings/mono/eina_mono/eina_inarray.cs b/src/bindings/mono/eina_mono/eina_inarray.cs
index b88570833d..6bb8626e8a 100644
--- a/src/bindings/mono/eina_mono/eina_inarray.cs
+++ b/src/bindings/mono/eina_mono/eina_inarray.cs
@@ -20,6 +20,7 @@ using System.Runtime.InteropServices;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Contracts;
 
 using static Eina.TraitFunctions;
 using static Eina.InarrayNativeFunctions;
@@ -485,6 +486,7 @@ public class Inarray<T> : IEnumerable<T>, IDisposable
     /// <returns>true on success, false otherwise.</returns>
     public bool Append(T[] values)
     {
+        Contract.Requires(values != null, nameof(values));
         foreach (T v in values)
         {
             if (Push(v) == -1)
diff --git a/src/bindings/mono/eina_mono/eina_inlist.cs b/src/bindings/mono/eina_mono/eina_inlist.cs
index cef686b469..3d2670e169 100644
--- a/src/bindings/mono/eina_mono/eina_inlist.cs
+++ b/src/bindings/mono/eina_mono/eina_inlist.cs
@@ -20,6 +20,7 @@ using System.Runtime.InteropServices;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Contracts;
 
 using static Eina.TraitFunctions;
 using static Eina.InlistNativeFunctions;
@@ -422,6 +423,7 @@ public class Inlist<T> : IEnumerable<T>, IDisposable
     /// <param name="values">The values to be added.</param>
     public void AppendArray(T[] values)
     {
+        Contract.Requires(values != null, nameof(values));
         foreach (T v in values)
         {
             Append(v);
diff --git a/src/bindings/mono/eina_mono/eina_list.cs b/src/bindings/mono/eina_mono/eina_list.cs
index 667b80834f..f4882d0afc 100644
--- a/src/bindings/mono/eina_mono/eina_list.cs
+++ b/src/bindings/mono/eina_mono/eina_list.cs
@@ -20,6 +20,7 @@ using System.Runtime.InteropServices;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Contracts;
 
 using static Eina.TraitFunctions;
 using static Eina.ListNativeFunctions;
@@ -533,6 +534,7 @@ public class List<T> : IList<T>, IEnumerable<T>, IDisposable
     /// <param name="values">The values to be appended.</param>
     public void Append(T[] values)
     {
+        Contract.Requires(values != null, nameof(values));
         RequireWritable();
 
         foreach (T v in values)
diff --git a/src/bindings/mono/eina_mono/eina_promises.cs b/src/bindings/mono/eina_mono/eina_promises.cs
index 4b14a0d894..9f725add3c 100644
--- a/src/bindings/mono/eina_mono/eina_promises.cs
+++ b/src/bindings/mono/eina_mono/eina_promises.cs
@@ -18,7 +18,7 @@ using System.Runtime.InteropServices;
 using System.Collections.Generic;
 using System.Linq;
 using System.ComponentModel;
-
+using System.Diagnostics.Contracts;
 
 using static Eina.EinaNative.PromiseNativeMethods;
 
@@ -207,6 +207,7 @@ public class Promise : IDisposable
     /// </summary>
     public void Resolve(Eina.Value value)
     {
+        Contract.Requires(value != null, nameof(value));
         SanityChecks();
         eina_promise_resolve(this.Handle, value);
         // Promise will take care of releasing this value correctly.
@@ -280,6 +281,7 @@ public class Future
     /// <param name="cb">The callback to be called when the attached promise resolves.</param>
     public Future(Promise promise, ResolvedCb cb = null)
     {
+        Contract.Requires(promise != null, nameof(promise));
         IntPtr intermediate = eina_future_new(promise.Handle);
         Handle = ThenRaw(intermediate, (Eina.Value value) =>
         {
diff --git a/src/bindings/mono/eina_mono/eina_slice.cs b/src/bindings/mono/eina_mono/eina_slice.cs
index e47da1071c..912ddea3bd 100644
--- a/src/bindings/mono/eina_mono/eina_slice.cs
+++ b/src/bindings/mono/eina_mono/eina_slice.cs
@@ -18,6 +18,7 @@
 using System;
 using System.Runtime.InteropServices;
 using System.ComponentModel;
+using System.Diagnostics.Contracts;
 
 namespace Eina
 {
@@ -235,6 +236,7 @@ public static class Eina_SliceUtils
 {
     public static byte[] GetBytes(this Eina.ISliceBase slc)
     {
+        Contract.Requires(slc != null, nameof(slc));
         var size = (int)(slc.Len);
         byte[] mArray = new byte[size];
         Marshal.Copy(slc.Mem, mArray, 0, size);
diff --git a/src/bindings/mono/eina_mono/eina_value.cs b/src/bindings/mono/eina_mono/eina_value.cs
index 5b203812da..46d1ff02b5 100644
--- a/src/bindings/mono/eina_mono/eina_value.cs
+++ b/src/bindings/mono/eina_mono/eina_value.cs
@@ -27,6 +27,7 @@ using System.Security;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.Serialization;
 using System.Globalization;
+using System.Diagnostics.Contracts;
 
 using static Eina.EinaNative.UnsafeNativeMethods;
 using static Eina.TraitFunctions;
@@ -1268,8 +1269,10 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <para>Since EFL 1.23.</para>
     /// </summary>
     /// <param name="obj">The object to be wrapped.</param>
+    [SuppressMessage("Microsoft.Design", "CA1062:ValidateArgumentsOfPublicMethods", Justification="Could not remove warning!")]
     public Value(object obj) : this()
     {
+        Contract.Requires(obj != null, nameof(obj));
         var objType = obj.GetType();
 
         if (objType == typeof(sbyte))
@@ -1424,6 +1427,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The value to be copied.</param>
     public Value(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         Handle = Alloc();
         if (!eina_value_copy(v.Handle, this.Handle))
         {
@@ -1615,7 +1619,11 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     public static implicit operator ValueNative(Value v) => ToValueNative(v);
 
     [EditorBrowsable(EditorBrowsableState.Never)]
-    public static ValueNative ToValueNative(Value v) => v.GetNative();
+    public static ValueNative ToValueNative(Value v)
+    {
+        Contract.Requires(v != null, nameof(v));
+        return v.GetNative();
+    }
 
     /// <summary>Implicit conversion from native struct representation to managed wrapper.
     /// <para>Since EFL 1.23.</para>
@@ -1655,6 +1663,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static byte ToByte(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         byte b;
         v.Get(out b);
 
@@ -1691,6 +1700,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static sbyte ToSByte(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         sbyte b;
         v.Get(out b);
 
@@ -1727,6 +1737,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static short ToInt16(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         short b;
         v.Get(out b);
 
@@ -1763,6 +1774,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static ushort ToUInt16(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         ushort b;
         v.Get(out b);
 
@@ -1800,6 +1812,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static int ToInt32(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         int b;
         v.Get(out b);
 
@@ -1836,6 +1849,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static uint ToUInt32(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         uint b;
         v.Get(out b);
 
@@ -1872,6 +1886,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static long ToInt64(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         long b;
         v.Get(out b);
 
@@ -1908,6 +1923,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static ulong ToUInt64(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         ulong b;
         v.Get(out b);
 
@@ -1944,6 +1960,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static float ToSingle(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         float b;
         v.Get(out b);
 
@@ -1980,6 +1997,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static double ToDouble(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         double b;
         v.Get(out b);
 
@@ -2016,6 +2034,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static string ToString(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         string b;
         v.Get(out b);
 
@@ -2171,6 +2190,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <param name="v">The <see cref="Value" /> to be converted.</param>
     public static Efl.Object ToObject(Value v)
     {
+        Contract.Requires(v != null, nameof(v));
         Efl.Object obj;
         v.Get(out obj);
 
@@ -2714,6 +2734,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <returns><c>true</c> if the value was successfully stored.</returns>
     public bool Set(Efl.Object value)
     {
+        Contract.Requires(value != null, nameof(value));
         SanityChecks();
 
         if (this.Optional)
@@ -2735,6 +2756,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <returns><c>true</c> if the value was successfully stored.</returns>
     public bool Set(Value value)
     {
+        Contract.Requires(value != null, nameof(value));
         OptionalSanityChecks();
         ValueType subtype = value.GetValueType();
 
@@ -3321,6 +3343,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
     /// <returns><c>true</c> if the value was successfully appended.</returns>
     public bool Append(object o)
     {
+        Contract.Requires(o != null, nameof(o));
         ContainerSanityChecks();
 
         switch (GetValueSubType())
@@ -3508,6 +3531,7 @@ public class Value : IDisposable, IComparable<Value>, IEquatable<Value>
         }
         set
         {
+            Contract.Requires(value != null, nameof(value));
             ContainerSanityChecks(i);
 
             switch (GetValueSubType())
@@ -3650,6 +3674,7 @@ public class ValueMarshaler : ICustomMarshaler
     /// keeping the managed ownership.</summary>
     public IntPtr MarshalManagedToNative(object managedObj)
     {
+        Contract.Requires(managedObj != null, nameof(managedObj));
         try
         {
             Value v = (Value)managedObj;
@@ -3703,6 +3728,7 @@ public class ValueMarshalerOwn : ICustomMarshaler
     /// when not needed. </summary>
     public IntPtr MarshalManagedToNative(object managedObj)
     {
+        Contract.Requires(managedObj != null, nameof(managedObj));
         try
         {
             Value v = (Value)managedObj;
diff --git a/src/bindings/mono/eldbus_mono/eldbus_common.cs b/src/bindings/mono/eldbus_mono/eldbus_common.cs
index 2606fe92c8..6ca2de007f 100644
--- a/src/bindings/mono/eldbus_mono/eldbus_common.cs
+++ b/src/bindings/mono/eldbus_mono/eldbus_common.cs
@@ -19,6 +19,7 @@ using System;
 using System.Runtime.InteropServices;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Contracts;
 
 using static eldbus.EldbusMessageNativeFunctions;
 
@@ -948,12 +949,14 @@ public class ByteMessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -997,12 +1000,14 @@ public class BoolMessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1046,12 +1051,14 @@ public class Int16MessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1095,12 +1102,14 @@ public class UInt16MessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1144,12 +1153,14 @@ public class Int32MessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1193,12 +1204,14 @@ public class UInt32MessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1242,12 +1255,14 @@ public class Int64MessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1291,12 +1306,14 @@ public class UInt64MessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1340,12 +1357,14 @@ public class DoubleMessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1371,12 +1390,14 @@ public abstract class StringLikeMessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
@@ -1522,12 +1543,14 @@ public class UnixFdMessageArgument : BasicMessageArgument
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.Message msg)
     {
+        Contract.Requires(msg != null, nameof(msg));
         return eldbus_message_arguments_append(msg.Handle, Signature, value);
     }
 
     [EditorBrowsable(EditorBrowsableState.Never)]
     protected override bool InternalAppendTo(eldbus.MessageIterator iter)
     {
+        Contract.Requires(iter != null, nameof(iter));
         return eldbus_message_iter_basic_append(iter.Handle, TypeCode, value);
     }
 }
diff --git a/src/bindings/mono/eldbus_mono/eldbus_message.cs b/src/bindings/mono/eldbus_mono/eldbus_message.cs
index 71baf6d83f..8ab48ba2bd 100644
--- a/src/bindings/mono/eldbus_mono/eldbus_message.cs
+++ b/src/bindings/mono/eldbus_mono/eldbus_message.cs
@@ -18,6 +18,7 @@
 using System;
 using System.Runtime.InteropServices;
 using System.ComponentModel;
+using System.Diagnostics.Contracts;
 
 using static eldbus.EldbusMessageNativeFunctions;
 
@@ -773,6 +774,7 @@ public class MessageIterator
     /// <returns>A <see cref="eldbus.MessageIterator" />.</returns>
     public eldbus.MessageIterator AppendOpenContainer(string signature)
     {
+        Contract.Requires(signature != null, nameof(signature));
         CheckHandle();
 
         IntPtr new_iter = IntPtr.Zero;
diff --git a/src/bindings/mono/eldbus_mono/eldbus_proxy.cs b/src/bindings/mono/eldbus_mono/eldbus_proxy.cs
index a3a984df97..8ed9bed82b 100644
--- a/src/bindings/mono/eldbus_mono/eldbus_proxy.cs
+++ b/src/bindings/mono/eldbus_mono/eldbus_proxy.cs
@@ -18,6 +18,7 @@
 using System;
 using System.Runtime.InteropServices;
 using System.ComponentModel;
+using System.Diagnostics.Contracts;
 
 using static eldbus.EldbusProxyNativeFunctions;
 
@@ -123,6 +124,7 @@ public class Proxy : IDisposable
     /// <param name="_interface">The interface name.</param>
     public Proxy(eldbus.Object obj, string _interface)
     {
+        Contract.Requires(obj != null, nameof(obj));
         InitNew(eldbus_proxy_get(obj.Handle, _interface), true);
     }