Github user kl0u commented on a diff in the pull request:
https://github.com/apache/flink/pull/3484#discussion_r106138895
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/transformations/SideOutputTransformation.java
---
@@ -0,0 +1,73 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.flink.streaming.api.transformations;
+
+import static java.util.Objects.requireNonNull;
+
+import com.google.common.collect.Lists;
+import org.apache.flink.util.OutputTag;
+import org.apache.flink.streaming.api.operators.ChainingStrategy;
+
+import java.util.Collection;
+import java.util.List;
+
+
+/**
+ * This transformation represents a selection of a side output of an
upstream operation with a
+ * given {@link OutputTag}.
+ *
+ * <p>This does not create a physical operation, it only affects how
upstream operations are
+ * connected to downstream operations.
+ *
+ * @param <T> The type of the elements that result from this {@code
SideOutputTransformation}
+ */
--- End diff --
Here we do not check if the `input` is `null` (we do it in the caller
method only) but we try get the parallelism. We could have the parallelism as a
separate argument, and then, after the `super()` check if the input is null.
This makes the code of the class self-contained as you do not have to check
other classes to see if the `input` can be `null` or not. What do you think?
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