Fix nullable in Equals() and ToString()

Parser/Internal/GreenNode.cs

@@ -74,11 +74,6 @@ namespace Parser.Internal
 
         internal bool IsMissing => _isMissing;
 
-        public override string ToString()
-        {
-            return base.ToString();
-        }
-
         private void WriteTo(TextWriter writer, bool leading, bool trailing)
         {
             var stack = new Stack<(GreenNode node, bool leading, bool trailing)>();

Parser/SyntaxToken.cs

@@ -12,7 +12,7 @@ namespace Parser
 
         public TokenKind Kind => _token.Kind;
 
-        public override string ToString()
+        public override string? ToString()
         {
             return _token.ToString();
         }
@@ -34,7 +34,7 @@ namespace Parser
             return Equals(_parent, other._parent) && Equals(_token, other._token);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (ReferenceEquals(null, obj)) return false;
             return obj is SyntaxToken token && Equals(token);

Parser/SyntaxTrivia.cs

@@ -22,7 +22,7 @@ namespace Parser
             return Equals(_parent, other._parent) && Equals(_trivia, other._trivia);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (ReferenceEquals(null, obj)) return false;
             return obj is SyntaxTrivia trivia && Equals(trivia);