private void checkConnectCalled() {
    if (gfManagerAgent == null) {
      throw new IllegalStateException(
          "connect() has not been invoked on this AdminDistributedSystem.");
    }
  }
Checks to make sure that {@link #connect()} has been called.

@throws IllegalStateException If {@link #connect()} has not been called.
geode-core/src/main/java/org/apache/geode/admin/internal/AdminDistributedSystemImpl.java