Best way to check for Json null values?

[xioren]

I have a situation where I recieve Json from the web and sometimes the "audio" 
key has a value and sometimes its "null". What would be the "proper" way to 
test "null"? I have:
    
    
    if $response["audio"] != "null":
      do stuff
    
    
    Run

but this doesn't seem right.