default ToByteNullable<ENTITY> asByte() {
        return mapToByteIfPresent(val -> {
            if (val instanceof Number) {
                final Number number = (Number) val;
                return number.byteValue();
            } else throw new SpeedmentFieldException(format(
                "Expected field %s to be of type byte, but it was not.",
                identifier()
            ));
        });
    }
Returns an {@link ToByteNullable} expression that has the value of this
field, casted to a {@code byte} by first casting it to {@link Number} and
then invoking {@link Number#byteValue()}.

@return  expression for this value after mapper has been applied

@since 3.1.0
runtime-parent/runtime-field/src/main/java/com/speedment/runtime/field/ReferenceField.java