False Negative : Statically non-null expressions are not reported by `RedundantNullCheck`

[Carlson-JLQ]

False Negative : Statically non-null expressions are not reported by RedundantNullCheck

Affects errorprone Version:

2.48.0

Checker:

RedundantNullCheck

Description:

The official RedundantNullCheck description says it reports null checks on expressions that are statically determined to be non-null. The following samples all fit that rule: final fields initialized with non-null literals, expressions proven non-null by control flow, and values whose construction makes null impossible.

Code Sample demonstrating the issue:

// PosCase2
private final String NAME = "constant";
if (NAME != null) {
    System.out.println("always true");
}

// PosCase3
private final String NAME = "constant";
if (Objects.isNull(NAME)) {
    System.out.println("impossible");
}

// PosCase4
Object obj = "string";
String casted = (String) obj;
if (casted == null) {
    System.out.println("impossible");
}

// PosCase6 / PosCase7
String result = flag ? "yes" : "no";
if (result == null) {
    System.out.println("impossible");
}
if (Objects.nonNull(result)) {
    System.out.println("always true");
}

// PosCase8 / PosCase9
if (s != null) {
    if (s == null) {
        System.out.println("impossible");
    }
}
if (obj != null) {
    if (Objects.nonNull(obj)) {
        System.out.println("always true");
    }
}

These examples are all redundant for the same reason: the checked expression is already known to be non-null, or already known to satisfy the opposite nullness fact, before the reported condition is evaluated.

Expected outcome:

Error Prone should report these redundant null checks, but it doesn't. This is a false-negative.