CHEF-4101: DeepMerge - support overwriting hash values with nil

2 files changed, 20 insertions, 3 deletions

diff --git a/lib/chef/mixin/deep_merge.rb b/lib/chef/mixin/deep_merge.rb
index a8a4737758..5e3327a526 100644
--- a/lib/chef/mixin/deep_merge.rb
+++ b/lib/chef/mixin/deep_merge.rb
@@ -29,7 +29,6 @@ class Chef
 
       class InvalidSubtractiveMerge < ArgumentError; end
 
-
       OLD_KNOCKOUT_PREFIX = "!merge:".freeze
 
       # Regex to match the "knockout prefix" that was used to indicate
@@ -86,8 +85,12 @@ class Chef
         when Hash
           if dest.kind_of?(Hash)
             source.each do |src_key, src_value|
-              if dest[src_key]
-                dest[src_key] = deep_merge!(src_value, dest[src_key])
+              if dest.has_key? src_key
+                if dest[src_key].nil?
+                  dest[src_key] = nil
+                else
+                  dest[src_key] = deep_merge!(src_value, dest[src_key])
+                end
               else # dest[src_key] doesn't exist so we take whatever source has
                 raise_if_knockout_used!(src_value)
                 dest[src_key] = src_value
diff --git a/spec/unit/mixin/deep_merge_spec.rb b/spec/unit/mixin/deep_merge_spec.rb
index 76f5c68a29..dbc49e68f2 100644
--- a/spec/unit/mixin/deep_merge_spec.rb
+++ b/spec/unit/mixin/deep_merge_spec.rb
@@ -236,6 +236,20 @@ describe Chef::Mixin::DeepMerge, "deep_merge!" do
     @dm.deep_merge!(hash_src, hash_dst)
     hash_dst.should == {"item" => "orange"}
   end
+
+  it 'should overwrite hashes with nil' do
+    hash_src = {"item" => { "1" => "2"}, "other" => true }
+    hash_dst = {"item" => nil }
+    @dm.deep_merge!(hash_src, hash_dst)
+    hash_dst.should == {"item" => nil, "other" => true }
+  end
+
+  it 'should overwrite strings with nil' do
+    hash_src = {"item" => "to_overwrite", "other" => false }
+    hash_dst = {"item" => nil }
+    @dm.deep_merge!(hash_src, hash_dst)
+    hash_dst.should == {"item" => nil, "other" => false }
+  end
 end # deep_merge!
 
 # Chef specific