@Override
    default Class<E> enumClass() {
        return innerNullable().enumClass();
    }
Specialized {@link NonNullableExpression} for {@code Enum} values where a
{@link NullPointerException} is thrown if the original expression returns
{@code null}.

@param <T> the input entity type
@param <E> the enum type

@author Emil Forslund
@since  3.1.0
runtime-parent/runtime-compute/src/main/java/com/speedment/runtime/compute/expression/orelse/ToEnumOrThrow.java