default ImplementAs getNullableImplementation() {
        final String impl = getAsString(HasNullableUtil.NULLABLE_IMPLEMENTATION).orElse(null);
        if (impl == null) {
            return ImplementAs.OPTIONAL;
        } else {
            return ImplementAs.valueOf(impl);
        }
    }
Returns the implementation that should be used when generating getters
for this column. If {@link ImplementAs#OPTIONAL}, every getter will
return an {@code Optional<T>}, {@code OptionalInt}, etc. If 
{@link ImplementAs#WRAPPER}, every getter will return the type as it is, 
{@code Long} for an example.
<p>
If no value is specified, {@link ImplementAs#OPTIONAL} is returned.

@return  the nullable implementation or {@link ImplementAs#OPTIONAL} if
         it is not specified
runtime-parent/runtime-config/src/main/java/com/speedment/runtime/config/trait/HasNullable.java