Fix NPE thrown by LRU Cache

When attempting to remove a non-existing entry from the LRU cache, the
underlying synchronized map will return 'null' rather than a Boolean.

The attempt to unbox 'null' as a primitive boolean was causing an NPE
to be thrown.

Fix this by changing the return type of the remove() method to Boolean.

Bug: Issue 14099
Change-Id: If4aca686ed0fe1e4ccc2ad58deb50694a343dc38

src/main/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRU.java

diff --git a/src/main/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRU.java b/src/main/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRU.java
index ac5183e..7f450d5 100644
--- a/src/main/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRU.java
+++ b/src/main/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRU.java
@@ -46,7 +46,13 @@
     return LRUMap.containsKey(key);
   }
 
-  public boolean remove(K key) {
+  /**
+   * Remove a key from the map
+   *
+   * @param key element to remove from the map
+   * @return true when key was in the map, null otherwise
+   */
+  public Boolean remove(K key) {
     return LRUMap.remove(key);
   }
 

src/test/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRUTest.java

diff --git a/src/test/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRUTest.java b/src/test/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRUTest.java
index af27216..3d435c9 100644
--- a/src/test/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRUTest.java
+++ b/src/test/java/com/googlesource/gerrit/modules/cache/chroniclemap/InMemoryLRUTest.java
@@ -42,4 +42,20 @@
 
     assertThat(map.toArray()).asList().containsExactly("B", "C");
   }
+
+  @Test
+  public void remove_unexistingEntryShouldReturnNull() {
+    InMemoryLRU<Object> map = new InMemoryLRU<>(1);
+
+    assertThat(map.remove("foo")).isNull();
+  }
+
+  @Test
+  public void remove_unexistingEntryShouldReturnTrue() {
+    InMemoryLRU<Object> map = new InMemoryLRU<>(1);
+
+    map.add("foo");
+
+    assertThat(map.remove("foo")).isTrue();
+  }
 }