This checker looks for comparisons of protocol buffer fields with null via the com.google.common.base.Preconditions.checkNotNull method. If a proto field is not specified, its field accessor will return a non-null default value. Thus, the result of calling one of these accessors can never be null, and comparisons like these often indicate a nearby error.

If you meant to check whether an optional field has been set, you should use the hasField() method instead.