code: @NonNull public static Flow get(@NonNull Context context) {
      Flow flow = InternalContextWrapper.getFlow(context);
      if (null == flow) {
        throw new IllegalStateException("Context was not wrapped with flow. "
            + "Make sure attachBaseContext was overridden in your main activity");
      }
      return flow;
    }
docs: Returns the Flow instance for the {@link Activity} that owns the given context.
  Note that it is not safe to call this method before the first call to that
  Activity's {@link Activity#onResume()} method in the current Android task. In practice
  this boils down to two rules:
  <ol>
  <li>In views, do not access Flow before {@link View#onAttachedToWindow()} is called.
  <li>In activities, do not access flow before {@link Activity#onResume()} is called.
  </ol>