ui: Prevent crashes due to null names in flamegraphs

Bug: 200138104
Change-Id: I681d19a86b7aaa71b338eb3845dcfce0ae061c7d
diff --git a/ui/src/controller/heap_profile_controller.ts b/ui/src/controller/heap_profile_controller.ts
index ef9df65..ecbbacc 100644
--- a/ui/src/controller/heap_profile_controller.ts
+++ b/ui/src/controller/heap_profile_controller.ts
@@ -273,7 +273,7 @@
     const callsites = await this.args.engine.query(`
         SELECT
         id as hash,
-        IFNULL(DEMANGLE(name), name) as name,
+        IFNULL(IFNULL(DEMANGLE(name), name), '[NULL]') as name,
         IFNULL(parent_id, -1) as parentHash,
         depth,
         cumulative_size as cumulativeSize,