[Fix #1630] Fix a false positive in Rails/StrongParametersExpect

[koic]

This PR fixes a false positive in Rails/StrongParametersExpect when negating params[:key] with !, such as !params[:key] or condition && !params[:key].

Negating params[:key] is a way of checking for an optional parameter, where a missing value is expected and should be falsy. Rewriting !params[:key] to !params.expect(:key) changes the runtime behavior, because params.expect(:key) raises ActionController::ParameterMissing when the parameter is absent instead of returning a falsy value.

Fixes #1630.

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