has_expr only mentions extra_env if it is not empty

Author: machow

pythonwhat/check_funcs.py

@@ -441,7 +441,7 @@ def parse_tree(n):
 
     return state
 
-def has_expr(incorrect_msg="FMT:Unexpected expression {test}: expected `{sol_eval}`, got `{stu_eval}` with values{extra_env}.",
+def has_expr(incorrect_msg="__JINJA__:Unexpected expression {{test}}: expected `{{sol_eval}}`, got `{{stu_eval}` {{'with values ' + extra_env if extra_env}}.",
              error_msg="Running an expression in the student process caused an issue.",
              undefined_msg="FMT:Have you defined `{name}` without errors?",
              extra_env=None,