if (! mObservers) return NS_OK;  mObservers->RemoveElement(aObserver);
InMemoryDataSource::RemoveObserver(nsIRDFObserver* aObserver){    NS_PRECONDITION(aObserver != nsnull, "null ptr");    if (! aObserver)        return NS_ERROR_NULL_POINTER;    NS_AUTOLOCK(mLock);    if (! mObservers)        return NS_OK;    mObservers->RemoveElement(aObserver);    return NS_OK;}