checker/tests/nullness/Synchronization.java

import org.checkerframework.checker.nullness.qual.*;

public class Synchronization {

  // Plain
  public void bad() {
    Object o = null;
    // :: error: (locking.nullable)
    synchronized (o) {
    } // should emit error
  }

  public void ok() {
    // NonNull specifically
    @NonNull Object o1 = "m";
    synchronized (o1) {
    }
  }

  public void flow() {
    Object o = null;
    o = "m";
    synchronized (o) {
    } // valid
    o = null;
    // :: error: (locking.nullable)
    synchronized (o) {
    } // invalid
  }

  public Synchronization() {
    synchronized (this) {
    }
  }
}