Only print a traceback if there is one to print

Author: kmvanbrunt

cmd2/cmd2.py

@@ -587,7 +587,7 @@ def perror(self, err: Union[str, Exception], traceback_war: bool = True, err_col
         :param err_color: (optional) color escape to output error with
         :param war_color: (optional) color escape to output warning with
         """
-        if self.debug:
+        if self.debug and sys.exc_info() != (None, None, None):
             import traceback
             traceback.print_exc()