Fix diff highlighting

Change-Id: Ie9de1677fa848c62ed01a092609219b3495f5609

polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
index 74164a8..859cf10 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
@@ -417,7 +417,7 @@
     offsetRight: number,
     row: string,
     i: number,
-    highlights: Highlights[] = []
+    highlights?: Highlights[]
   ): GrDiffLine {
     const line = new GrDiffLine(type);
     line.text = row;