Add missing copyright/license header

Change-Id: I70c39bc46000f062f2e1fa7783da8fb521e31b6a

src/main/java/com/googlesource/gerrit/plugins/task/TaskExpressionKey.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskExpressionKey.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskExpressionKey.java
index 69afd26..0a05b2e 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/TaskExpressionKey.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskExpressionKey.java
@@ -1,3 +1,17 @@
+// Copyright (C) 2022 The Android Open Source Project
+//
+// 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.googlesource.gerrit.plugins.task;
 
 import com.google.auto.value.AutoValue;