fix issue #109 and #110

issue 109: None not represented round-trippable at top level, reported by
Andrea Censi
issue 110: .replace() on a ScalarString subclass would return a string instead
of an instance of that subclass, reported by sandres23

6 files changed, 87 insertions, 4 deletions

diff --git a/README.rst b/README.rst
index 560161e..b82244b 100644
--- a/README.rst
+++ b/README.rst
@@ -18,6 +18,11 @@ ChangeLog
 
 .. should insert NEXT: at the beginning of line for next key
 
+NEXT:
+  - fix issue 109: None not dumping correctly at top level (reported by Andrea Censi)
+  - fix issue 110: .replace on Preserved/DoubleQuoted/SingleQuoted ScalarString
+    would give back "normal" string (reported by sandres23)
+
 0.14.4 (2017-03-31):
   - fix readme
 
diff --git a/__init__.py b/__init__.py
index b3fe1a0..3fdcb33 100644
--- a/__init__.py
+++ b/__init__.py
@@ -10,8 +10,8 @@ from typing import Dict, Any  # NOQA
 
 _package_data = dict(
     full_package_name='ruamel.yaml',
-    version_info=(0, 14, 4),
-    __version__='0.14.4',
+    version_info=(0, 14, 5, 'dev'),
+    __version__='0.14.5.dev',
     author='Anthon van der Neut',
     author_email='a.van.der.neut@ruamel.eu',
     description='ruamel.yaml is a YAML parser/emitter that supports roundtrip preservation of comments, seq/map flow style, and map key order',  # NOQA
diff --git a/_test/test_none.py b/_test/test_none.py
new file mode 100644
index 0000000..ad51109
--- /dev/null
+++ b/_test/test_none.py
@@ -0,0 +1,42 @@
+# coding: utf-8
+
+
+import pytest    # NOQA
+import ruamel.yaml   # NOQA
+
+
+class TestNone:
+    def test_dump00(self):
+        data = None
+        s = ruamel.yaml.round_trip_dump(data)
+        assert s == 'null\n...\n'
+        d = ruamel.yaml.round_trip_load(s)
+        assert d == data
+
+    def test_dump01(self):
+        data = None
+        s = ruamel.yaml.round_trip_dump(data, explicit_end=True)
+        assert s == 'null\n...\n'
+        d = ruamel.yaml.round_trip_load(s)
+        assert d == data
+
+    def test_dump02(self):
+        data = None
+        s = ruamel.yaml.round_trip_dump(data, explicit_end=False)
+        assert s == 'null\n...\n'
+        d = ruamel.yaml.round_trip_load(s)
+        assert d == data
+
+    def test_dump03(self):
+        data = None
+        s = ruamel.yaml.round_trip_dump(data, explicit_start=True)
+        assert s == '---\n...\n'
+        d = ruamel.yaml.round_trip_load(s)
+        assert d == data
+
+    def test_dump04(self):
+        data = None
+        s = ruamel.yaml.round_trip_dump(data, explicit_start=True, explicit_end=False)
+        assert s == '---\n...\n'
+        d = ruamel.yaml.round_trip_load(s)
+        assert d == data
diff --git a/_test/test_string.py b/_test/test_string.py
index 13474b5..6b3070f 100644
--- a/_test/test_string.py
+++ b/_test/test_string.py
@@ -17,6 +17,7 @@ and the chomping modifiers:
 
 import pytest
 import platform
+import ruamel
 
 # from ruamel.yaml.compat import ordereddict
 from roundtrip import round_trip, dedent, round_trip_load, round_trip_dump  # NOQA
@@ -124,3 +125,33 @@ class TestQuotedScalarString:
         """, outp="""
         a: abc
         """)
+
+
+class TestReplace:
+    """inspired by issue 110 from sandres23"""
+    def test_replace_preserved_scalar_string(self):
+        s = dedent("""\
+        foo: |
+          foo
+          foo
+          bar
+          foo
+        """)
+        data = round_trip_load(s, preserve_quotes=True)
+        so = data['foo'].replace('foo', 'bar', 2)
+        assert isinstance(so, ruamel.yaml.scalarstring.PreservedScalarString)
+        assert so == dedent("""
+        bar
+        bar
+        bar
+        foo
+        """)
+
+    def test_replace_double_quoted_scalar_string(self):
+        s = dedent("""\
+        foo: "foo foo bar foo"
+        """)
+        data = round_trip_load(s, preserve_quotes=True)
+        so = data['foo'].replace('foo', 'bar', 2)
+        assert isinstance(so, ruamel.yaml.scalarstring.DoubleQuotedScalarString)
+        assert so == 'bar bar bar foo'
diff --git a/representer.py b/representer.py
index a64d825..5db1d98 100644
--- a/representer.py
+++ b/representer.py
@@ -644,8 +644,10 @@ class RoundTripRepresenter(SafeRepresenter):
 
     def represent_none(self, data):
         # type: (Any) -> Any
-        return self.represent_scalar(u'tag:yaml.org,2002:null',
-                                     u'')
+        if len(self.represented_objects) == 0 and not self.serializer.use_explicit_start:
+            # this will be open ended (although it is not yet)
+            return self.represent_scalar(u'tag:yaml.org,2002:null', u'null')
+        return self.represent_scalar(u'tag:yaml.org,2002:null', u'')
 
     def represent_preserved_scalarstring(self, data):
         # type: (Any) -> Any
diff --git a/scalarstring.py b/scalarstring.py
index b02ad1d..6689911 100644
--- a/scalarstring.py
+++ b/scalarstring.py
@@ -21,6 +21,9 @@ class ScalarString(text_type):
         # type: (Any, Any) -> Any
         return text_type.__new__(cls, *args, **kw)  # type: ignore
 
+    def replace(self, old, new, maxreplace=-1):
+        return type(self)((text_type.replace(self, old, new, maxreplace)))
+
 
 class PreservedScalarString(ScalarString):
     __slots__ = ()