[refactor-prompt] fix exception in specific help case

neo/Prompt/CommandBase.py

@@ -112,10 +112,11 @@ def __print_absolute_cmd_help(self):
             params += f"{p.formatted_name()} "
         print(f"\nUsage: {self.__command_with_parents()} {params}\n")
 
-        min_indent = 15
-        longest_param_name = max(min_indent, max(len(p.name) for p in self.command_desc().params))
-        for p in self.command_desc().params:
-            print(p.to_str(longest_param_name))
+        if len(self.command_desc().params) > 0:
+            min_indent = 15
+            longest_param_name = max(min_indent, max(len(p.name) for p in self.command_desc().params))
+            for p in self.command_desc().params:
+                print(p.to_str(longest_param_name))
 
     def __command_with_parents(self):
         s = self.command_desc().command