Check for None

[muellerzr]

What does this PR do?

The CV models test showed a failure when args is defined but kwargs are none (why only them, unsure as gpt2 didn't face this, but I digress). This check makes sure that the padding is only checked for if the value is not None (otherwise we get an error about how we can't run it w/o a tensor-like item)

Fixes # (issue)

Failing test on main

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@SunMarc

[SunMarc]

LGTM !

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