human
Solve the following python programming problem given the following code:
def null_safe(rule) : 
    ' Return original expr if rule returns None ' 
    def null_safe_rl(expr) : 
        result = rule (expr) 
        if (result is None) : 
            return expr 
else : 
            return result 
return rule 

    
    

    Fix the buggy line: return rule
assistant
#Here is Python program to fix the buggy line: return rule
.

return def null_safe_rl(