add null check for functionArgs in CallResetPasswordFunctionAsync

[JacobOscarGunnarsson]

Description

passing null as third arg will now throw a more descriptive ArgumentNullException error

Fixes #3011

[papafe]

The code looks nice, you just need to add a Changelog

[LaPeste]

After adding the entry in the changelog, for me it's good to go.

[nirinchev]

Let's add a small test to ensure it works and we don't break it in the future.

[papafe]

@nirinchev Given that we don't have tests for any of the null checks for methods in that class, I've suggested @JacobOscarGunnarsson to avoid adding one just for this. It's better if we create a ticket to add them all together