FALSE POSITIVE: contradictory instanceof checks make a null branch infeasible

Rules and Languages Report False-positive / False-negative...
1

Hi, I found a false positive in SonarQube 26.7.0 with sonar-java 8.34 when contradictory instanceof checks make a null branch infeasible.

Affected tool

SonarQube 26.7.0.124771; sonar-java 8.34 (build 44906)

Affected checker

SonarQube java:S2259

Minimal reproducer

class S2259ContradictoryInstanceof {
  void test(Object value) {
    if (value instanceof String && !(value instanceof Object)) {
      Object object = null;
      object.toString();
    }
  }
}

Reproduction command

sonar-scanner --version
sonar-scanner -Dsonar.projectKey=s2259-reproducer -Dsonar.sources=sonarqube-s2259-fp-contradictory-instanceof.java -Dsonar.host.url="$SONAR_HOST_URL" -Dsonar.token="$SONAR_TOKEN"

Current behavior

SonarQube reports sonarqube-s2259-fp-contradictory-instanceof.java:5: java:S2259: A NullPointerException could be thrown; object is nullable here.

Expected behavior

S2259 should not report this dereference. A String is always an Object, so the conjunction guarding the dereference cannot be true.