code: public <OUT> DataStreamSource<OUT> fromCollection(Collection<OUT> data, TypeInformation<OUT> typeInfo) {
  		Preconditions.checkNotNull(data, "Collection must not be null");
  
  		// must not have null elements and mixed elements
  		FromElementsFunction.checkCollection(data, typeInfo.getTypeClass());
  
  		SourceFunction<OUT> function;
  		try {
  			function = new FromElementsFunction<>(typeInfo.createSerializer(getConfig()), data);
  		}
  		catch (IOException e) {
  			throw new RuntimeException(e.getMessage(), e);
  		}
  		return addSource(function, "Collection Source", typeInfo).setParallelism(1);
  	}
docs: Creates a data stream from the given non-empty collection.
  
  <p>Note that this operation will result in a non-parallel data stream source,
  i.e., a data stream source with parallelism one.
  
  @param data
  The collection of elements to create the data stream from
  @param typeInfo
  The TypeInformation for the produced data stream
  @param <OUT>
  The type of the returned data stream
  @return The data stream representing the given collection