fix: Handle missing where_clause in IdentifierFromFile

Author: elifarley

src/cedarscript_ast_parser/cedarscript_ast_parser.py

@@ -137,7 +137,7 @@ def as_marker(self) -> Marker:
         return Marker(self.identifier_type, self.name or self.where_clause.value, self.offset)
 
     def __str__(self):
-        wc = self.where_clause
+        wc = self.where_clause or ''
         if wc:
             wc = f' ({wc})'
         result = f"{str(self.identifier_type).lower()} {self.name}{wc}"