BlameCacheImpl: Avoid NPE if path does not exist

Bug: Issue 5082
Change-Id: I46221926525f203fb8715f0e8e3e4e14c9b7a452

java/com/google/gitiles/blame/cache/BlameCacheImpl.java

diff --git a/java/com/google/gitiles/blame/cache/BlameCacheImpl.java b/java/com/google/gitiles/blame/cache/BlameCacheImpl.java
index 320bf49..75ab09b 100644
--- a/java/com/google/gitiles/blame/cache/BlameCacheImpl.java
+++ b/java/com/google/gitiles/blame/cache/BlameCacheImpl.java
@@ -136,6 +136,9 @@
   public static List<Region> loadBlame(Key key, Repository repo) throws IOException {
     try (BlameGenerator gen = new BlameGenerator(repo, key.path)) {
       gen.push(null, key.commitId);
+      if (gen.getResultContents() == null) {
+        return ImmutableList.of();
+      }
       return loadRegions(gen);
     }
   }