Fix PostgreSQL Cidr#change?: NoMethodError: undefined method `prefix` for nil

activerecord/lib/active_record/connection_adapters/postgresql/oid/cidr.rb

@@ -31,7 +31,7 @@ module ActiveRecord
           # TODO: Remove when IPAddr#== compares IPAddr#prefix. See
           # https://github.com/ruby/ipaddr/issues/21
           def changed?(old_value, new_value, _new_value_before_type_cast)
-            super || old_value.prefix != new_value.prefix
+            super || !old_value.nil? && old_value.prefix != new_value.prefix
           end
 
           def cast_value(value)

activerecord/test/cases/adapters/postgresql/cidr_test.rb

@@ -21,6 +21,15 @@ module ActiveRecord
 
           assert_equal "foo", type.serialize("foo")
         end
+
+        test "changed? with nil values" do
+          type = OID::Cidr.new
+
+          assert_not type.changed?(nil, nil, "")
+          assert type.changed?("192.168.0.0/24", nil, "")
+          assert type.changed?(nil, "192.168.0.0/24", "")
+          assert type.changed?("192.168.0.0/24", "192.168.0.0/25", "")
+        end
       end
     end
   end