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) {
        }
    }
}