Remove is_json Call

[davidvonthenen]

What is the current behavior?

Reported by @jjmaldonis:
I think the is_json method in helpers.py should be removed and the calling-code should be updated to use try/except. When is_json returns True, the json data gets deserialized twice: once by is_json and a 2nd time by the calling code. JSON deserialization is quite slow, so only running it once should make a noticeable difference (although I guess the HTTP requests will probably always by 100x slower, so ... maybe ignore ... but it's likely to be a criticism of anyone reading the code).

Steps to reproduce

NA

Expected behavior

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Please tell us about your environment

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Other information

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[davidvonthenen]

This PR should address this issue. We handle the JSON exception inline with the other ones.
#182