code: private static String getHostnamesFromInstances(Iterable<TaskManagerLocation> locations) {
  		StringBuilder bld = new StringBuilder();
  
  		boolean successive = false;
  		for (TaskManagerLocation loc : locations) {
  			if (successive) {
  				bld.append(", ");
  			} else {
  				successive = true;
  			}
  			bld.append(loc.getHostname());
  		}
  
  		return bld.toString();
  	}
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