Have `IntegerNodeBase` use an `Optional` to store its value rather than storing a separate `m_null` flag.
Have `IntegerNodeBase` use an `Optional` to store its value rather than
storing a separate `m_null` flag.

realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core