Method with Optional return type must not return null JAVA-S0031

The usage of an Optional return type (java.util.Optional or com.google.common.base.Optional for Java 7) always means that explicit null returns were not desired by design.

Examples

Bad Practice

public Optional<Boolean> checkSomething() {
    Optional<Boolean> retVal = null;

    if (something) {
        boolean boolValue = ...;
        retVal = Optional.of(boolValue);
    }

    return retVal; // May be null!
}

Returning a null value in such a case is a contract violation and will most likely break client code. In addition, this introduces the danger of encountering a null pointer exception in scenarios which expressly wish to prevent them.

Always initialize Optionals with the value returned by Optional.empty() instead of initializing to null:

Recommended

Optional<Boolean> retVal = Optional<>.empty();

if (something) {
    boolean boolValue = ...;
    retVal = Optional.of(boolValue);
}

return retVal; // retVal is now either empty or boolean valued; never null.

References

• JavaDoc for Optional
• CWE-476 - Null Pointer Dereference
• CWE-690 - Unchecked Return Value to NULL Pointer Dereference
• Spotbugs - NP_OPTIONAL_RETURN_NULL