Fix Some Potential NPE

public ViewMetadata getView(String keyspaceName, String viewName)
{
    assert keyspaceName != null;
    KeyspaceMetadata ksm = keyspaces.getNullable(keyspaceName);
    return (ksm == null) ? null : ksm.views.getNullable(viewName);//may return null
}

public static void announceViewDrop(String ksName, String viewName, boolean announceLocally) throws ConfigurationException
{
   ViewMetadata view = Schema.instance.getView(ksName, viewName);
    if (view == null)//null pointer checker
        throw new ConfigurationException(String.format("Cannot drop non existing materialized view '%s' in keyspace '%s'.", viewName,     ksName));
   KeyspaceMetadata ksm = Schema.instance.getKeyspaceMetadata(ksName);

   logger.info("Drop table '{}/{}'", view.keyspace, view.name);
   announce(SchemaKeyspace.makeDropViewMutation(ksm, view, FBUtilities.timestampMicros()), announceLocally);
}

if (current == null)
    throw new InvalidRequestException("There is no materialized view in keyspace " + keyspace());