code: public ExecutionVertex getGroupMember(final int pos) {
  
  		if (pos < 0) {
  			throw new IllegalArgumentException("Argument pos must be greater or equal to 0");
  		}
  
  		try {
  			return this.groupMembers.get(pos);
  		} catch (ArrayIndexOutOfBoundsException e) {
  			return null;
  		}
  	}
docs: Returns a specific execution vertex from the list of members.
  
  @param pos
  The position of the execution vertex to be returned.
  @return The execution vertex at position <code>pos</code> of the member list, <code>null</code> if there is no
  such position.