Fixed first token recognition when creating bnf concepts

src/parsers/SyaNodeParser.py

@@ -313,7 +313,6 @@ class InFixToPostFix:
         """
         return len(self.stack) > 0 and isinstance(self.stack[-1], type)
 
-
     def _make_source_code_with_concept(self, start, rpar_token, end):
         """
 
@@ -1068,6 +1067,10 @@ class SyaNodeParser(BaseNodeParser):
         :param parser_input:
         :return:
         """
+
+        if not isinstance(parser_input, ParserInput):
+            return None
+
         if parser_input.is_empty():
             return context.sheerka.ret(
                 self.name,