Fix bug where the string "null" (without quotes) is deserialized as a string, instead of null.

src/singledocparser.cpp

@@ -76,6 +76,12 @@ namespace YAML
 		
 		const Token& token = m_scanner.peek();
 
+        if(token.type == Token::PLAIN_SCALAR && token.value == "null") {
+            eventHandler.OnNull(mark, anchor);
+            m_scanner.pop();
+            return;
+        }
+		
 		// add non-specific tags
 		if(tag.empty())
 			tag = (token.type == Token::NON_PLAIN_SCALAR ? "!" : "?");

test/core/parsertests.cpp

@@ -28,6 +28,18 @@ namespace Test
             EXPECT_DOC_END();
             DONE();
         }
+
+        TEST NullStringScalar()
+        {
+            HANDLE("foo: null");
+            EXPECT_DOC_START();
+            EXPECT_MAP_START("?", 0);
+            EXPECT_SCALAR("?", 0, "foo");
+            EXPECT_NULL(0);
+            EXPECT_MAP_END();
+            EXPECT_DOC_END();
+            DONE();
+        }
     }
     
 	namespace {
@@ -57,6 +69,7 @@ namespace Test
 		int total = 0;
 		RunParserTest(&Parser::NoEndOfMapFlow, "No end of map flow", passed, total);
 		RunParserTest(&Parser::PlainScalarStartingWithQuestionMark, "Plain scalar starting with question mark", passed, total);
+		RunParserTest(&Parser::NullStringScalar, "Null string scalar", passed, total);
 		
 		std::cout << "Parser tests: " << passed << "/" << total << " passed\n";
 		return passed == total;