Import code from internal repository to git

java/com/google/domain/registry/mapreduce/NullInput.java

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+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Licensed 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 com.google.domain.registry.mapreduce;
+
+import com.google.appengine.tools.mapreduce.Input;
+import com.google.appengine.tools.mapreduce.InputReader;
+import com.google.common.collect.ImmutableList;
+
+import java.util.List;
+import java.util.NoSuchElementException;
+
+/** An input that returns a single {@code null} value. */
+public class NullInput<T> extends Input<T> {
+
+  private static final long serialVersionUID = 1816836937031979851L;
+
+  private static final class NullReader<T> extends InputReader<T> {
+
+    private static final long serialVersionUID = -8176201363578913125L;
+
+    boolean read = false;
+
+    @Override
+    public T next() throws NoSuchElementException {
+      if (read) {
+        throw new NoSuchElementException();
+      }
+      read = true;
+      return null;
+    }
+
+    @Override
+    public Double getProgress() {
+      return read ? 1.0 : 0.0;
+    }
+  }
+
+  @Override
+  public List<? extends InputReader<T>> createReaders() {
+    return ImmutableList.of(new NullReader<T>());
+  }
+}