Fix: Empty reveal locals ouput (#12400)

Fixes #12388

Co-authored-by: Cibin Mathew <cibinmathew@users.noreply.github.com>

mypy/messages.py

@@ -1171,9 +1171,12 @@ def reveal_locals(self, type_map: Dict[str, Optional[Type]], context: Context) -
  # To ensure that the output is predictable on Python < 3.6,
  # use an ordered dictionary sorted by variable name
  sorted_locals = OrderedDict(sorted(type_map.items(), key=lambda t: t[0]))
- self.note("Revealed local types are:", context)
- for line in [' {}: {}'.format(k, v) for k, v in sorted_locals.items()]:
- self.note(line, context)
+ if sorted_locals:
+ self.note("Revealed local types are:", context)
+ for k, v in sorted_locals.items():
+ self.note(' {}: {}'.format(k, v), context)
+ else:
+ self.note("There are no locals to reveal", context)
 
  def unsupported_type_type(self, item: Type, context: Context) -> None:
  self.fail('Cannot instantiate type "Type[{}]"'.format(format_type_bare(item)), context)