human
Solve the following python programming problem given the following code:
def has_at_least_one_key(* keys) : 
    'Validator that at least one key exists.' 
    def validate(obj) : 
        'Test keys exist in dict.' 
        if (not isinstance (obj, dict)) : 
            raise vol.Invalid ('expected dictionary') 
for k in obj.keys () : 
            if (k in keys) : 
                return obj 
raise vol.Invalid ('must contain one of {}.'.format (', '.join (keys))) 
return keys 

    
    

    Fix the buggy line: return keys
assistant
#Here is Python code to fix the buggy line: return keys
.

return def validate(