Consider removing findbugs exclusions for null pointer problems

There are suppressions for NP_NULL_ON_SOME_PATH_FROM_RETURN_VALUE in many places in the code with SuppressFBWarnings annotations.

https://spotbugs.readthedocs.io/en/stable/bugDescriptions.html#np-possible-null-pointer-dereference-due-to-return-value-of-called-method-np-null-on-some-path-from-return-value