Allow comparing with nil using operators such as "!="

[noahmillerj]

Firestore allows comparing with nil using "!=". I verified this in console. However the same query fails when performed with golang api. The enforcement on the operators used when comparing with nil value doesn't make sense.

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[bhshkh]

Please create an issue demonstrating the bug and link the issue with this PR Modify commit message to conventional commits https://www.conventionalcommits.org/en/v1.0.0/#summary

[bhshkh]

Closing this old PR as there is no linked bug.