public <OUT> DataStreamSource<OUT> addSource(SourceFunction<OUT> function, String sourceName) {
		return addSource(function, sourceName, null);
	}
public < OUT > DataStreamSource < OUT > addSource ( SourceFunction < OUT > function , String sourceName ) { return addSource ( function , sourceName , null ) ; }
Adds a data source with a custom type information thus opening a
{@link DataStream}. Only in very special cases does the user need to
support type information. Otherwise use
{@link #addSource(org.apache.flink.streaming.api.functions.source.SourceFunction)}

@param function
the user defined function
@param sourceName
Name of the data source
@param <OUT>
type of the returned stream
@return the data stream constructed