Guess 1: null check is missing; Guess 2: ternary does the appropriate check

amcasey · amcasey · commit 95b5a691d4b6 · 2017-05-31T16:30:27.000-07:00
diff --git a/src/server/project.ts b/src/server/project.ts
@@ -646,7 +646,7 @@ namespace ts.server {
 
                 const added: string[] = [];
                 const removed: string[] = [];
-                const updated: string[] = arrayFrom(updatedFileNames.keys());
+                const updated: string[] = updatedFileNames ? arrayFrom(updatedFileNames.keys()) : [];
 
                 forEachKey(currentFiles, id => {
                     if (!lastReportedFileNames.has(id)) {
