### Question:
ToByteNullableImpl implements NullableExpression<T, ToByte<T>>, ToByteNullable<T> { @Override public ToByteNullable<T> mapIfPresent(ByteUnaryOperator mapper) { return t -> isNull.test(t) ? null : mapper.applyAsByte(original.applyAsByte(t)); } ToByteNullableImpl(ToByte<T> original, Predicate<T> isNull); @Override ToByte<T> inner(); @Override Predicate<T> isNullPredicate(); @Override Byte apply(T t); @Override byte applyAsByte(T t); @Override ToByte<T> orThrow(); @Override ToByte<T> orElseGet(ToByte<T> getter); @Override ToByte<T> orElse(Byte value); @Override ToDoubleNullable<T> mapToDoubleIfPresent(ByteToDoubleFunction mapper); @Override ToByteNullable<T> mapIfPresent(ByteUnaryOperator mapper); @Override long hash(T object); @Override int compare(T first, T second); @Override boolean isNull(T object); @Override boolean isNotNull(T object); @Override boolean equals(Object o); @Override int hashCode();  }### Answer:
@Test void mapIfPresent() { ToByteNullable<String> toByteNullable = instance.mapIfPresent(b -> (byte) 0); assertNotNull(toByteNullable); assertEquals(0, toByteNullable.applyAsByte("1")); assertNull(toByteNullable.apply(null)); }