@GwtIncompatible // NullPointerTester
  public void testNullPointers() {
    /*
     * Don't bother testing: Preconditions defines a bunch of methods that accept a template (or
     * even entire message) that simultaneously:
     *
     * - _shouldn't_ be null, so we don't annotate it with @Nullable
     *
     * - _can_ be null without causing a runtime failure (because we don't want the interesting

  @GwtIncompatible // NullPointerTester
  public void testNullPointers() {
    /*
     * Don't bother testing: Preconditions defines a bunch of methods that accept a template (or
     * even entire message) that simultaneously:
     *
     * - _shouldn't_ be null, so we don't annotate it with @Nullable
     *
     * - _can_ be null without causing a runtime failure (because we don't want the interesting

        // this can be safely acquired after the acquiredLock.
        //
        // Note that there is a race condition here which can result in missing
        // a cyclic edge: it's possible for two threads to simultaneous find
        // "safe" edges which together form a cycle. Preventing this race
        // condition efficiently without _introducing_ deadlock is probably

    cache.put(key, "1");
    // simultaneous update for same key, some null, some non-null
    doParallelCacheOp(
        count,
        n -> {
          cache.asMap().compute(key, (k, v) -> n % 2 == 0 ? v + delimiter + n : null);
        });
    assertTrue(1 >= cache.size());
  }

  public void testCompute() {
    cache.put(key, "1");
    // simultaneous deletion
    doParallelCacheOp(
        count,