OperatorNullPropagation : added code + unit-tests (#100)

Author: StefH

src/System.Linq.Dynamic.Core/ClassFactory.cs

@@ -895,6 +895,10 @@ Expression ParsePrimary()
                     _textParser.NextToken();
                     expr = ParseMemberAccess(null, expr);
                 }
+                else if (_textParser.CurrentToken.Id == TokenId.NullPropagation)
+                {
+                    throw new NotSupportedException("An expression tree lambda may not contain a null propagating operator");
+                }
                 else if (_textParser.CurrentToken.Id == TokenId.OpenBracket)
                 {
                     expr = ParseElementAccess(expr);

src/System.Linq.Dynamic.Core/ExpressionParser.cs

@@ -214,6 +214,11 @@ public void NextToken()
                         NextChar();
                         tokenId = TokenId.NullCoalescing;
                     }
+                    else if (_ch == '.')
+                    {
+                        NextChar();
+                        tokenId = TokenId.NullPropagation;
+                    }
                     else
                     {
                         tokenId = TokenId.Question;

src/System.Linq.Dynamic.Core/GeneratedTypesCache.cs

@@ -39,6 +39,7 @@ internal enum TokenId
         DoubleGreaterThan,
         DoubleLessThan,
         NullCoalescing,
-        Lambda
+        Lambda,
+        NullPropagation
     }
 }