@Override
    public TypeMapper<D, V> typeMapper() {
        return typeMapper;
    }
@param <ENTITY> the entity type
@param <D>      the database type
@param <V>      the field value type

@author  Per Minborg
@author  Emil Forslund
@since   2.2.0
runtime-parent/runtime-field/src/main/java/com/speedment/runtime/field/internal/ReferenceFieldImpl.java