do not pass nil values to arel

activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb

@@ -79,7 +79,7 @@ def delete_records(records)
           else
             relation = Arel::Table.new(@reflection.options[:join_table])
             relation.where(relation[@reflection.primary_key_name].eq(@owner.id).
-              and(relation[@reflection.association_foreign_key].in(records.map { |x| x.id }))
+              and(relation[@reflection.association_foreign_key].in(records.map { |x| x.id }.compact))
             ).delete
           end
         end