Add missing `:nodoc:`

We're accidentally documenting `PredicateBuilder` and `ArrayHandler`
since there's a constant which is missing `# :nodoc:`

activerecord/lib/active_record/relation/predicate_builder/array_handler.rb

@@ -27,7 +27,7 @@ def call(attribute, value)
         array_predicates.inject { |composite, predicate| composite.or(predicate) }
       end
 
-      module NullPredicate
+      module NullPredicate # :nodoc:
         def self.or(other)
           other
         end