Error: Invalid argument passed to canTransform argument source_frame

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Hi,

I'm using the Euclidean Clustering and trying to publish a certain cluster which has 3500- 4500 points in it, but iI'm getting a weird error when trying to visualize it in rviz.

[WARN] [1426601373.806774699]: Invalid argument passed to canTransform argument source_frame in tf2 frame_ids cannot be empty

It works fine when I use the original cloud, the problem seems to be with the cloudCluster. Here is the code:

pcl::PointCloud<pcl::PointXYZ> cloudCluster;
for (std::vector<pcl::PointIndices>::const_iterator it = cluster_indices.begin (); it != cluster_indices.end (); ++it)
{
  pcl::PointCloud<pcl::PointXYZ>::Ptr cloud_cluster (new pcl::PointCloud<pcl::PointXYZ>);
  for (std::vector<int>::const_iterator pit = it->indices.begin (); pit != it->indices.end (); ++pit)
  {
    cloud_cluster->points.push_back (cloud_filtered->points[*pit]);
  }

  cloud_cluster->width = cloud_cluster->points.size ();
  cloud_cluster->height = 1;
  cloud_cluster->is_dense = true;


  if (cloud_cluster->points.size() > 3500 && cloud_cluster->points.size() < 4500) {
    cloudCluster = *cloud_cluster;
  }
  j++;
}
sensor_msgs::PointCloud2 cloud2;
pcl::toROSMsg(cloudCluster, cloud2);

pub_.publish(cloud2);