IssueTracker

Component used: Fragment
Version used: androidx.fragment:fragment:1.2.0
Devices/Android versions reproduced on:

Calling FragmentManager toString() when it is not attached to an Activity crashes with NPE since mHost is null here:

    @NonNull
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(128);
        sb.append("FragmentManager{");
        sb.append(Integer.toHexString(System.identityHashCode(this)));
        sb.append(" in ");
        if (mParent != null) {
            Class<?> cls = mParent.getClass();
            sb.append(cls.getSimpleName());
            sb.append("{");
            sb.append(Integer.toHexString(System.identityHashCode(mParent)));
            sb.append("}");
        } else {
            Class<?> cls = mHost.getClass();
            sb.append(cls.getSimpleName());
            sb.append("{");
            sb.append(Integer.toHexString(System.identityHashCode(mHost)));
            sb.append("}");
        }
        sb.append("}}");
        return sb.toString();
    }

Originally detected with a dirty hack of dump()ing a Fragment to detect if it's in backstack or not, as in https://github.com/sockeqwe/mosby/issues/318#issuecomment-433439830