[tools] Filter empty categories in GC eval script

tools/eval_gc_nvp.py

Index: tools/eval_gc_nvp.py
diff --git a/tools/eval_gc_nvp.py b/tools/eval_gc_nvp.py
index af131f182fc52f71b8b741c43bcba05d60b3bf06..fcb6d8b9a2232ff24b04709d9520df0bd0b61755 100755
--- a/tools/eval_gc_nvp.py
+++ b/tools/eval_gc_nvp.py
@@ -97,6 +97,9 @@ class Category:
       return 0.0
     return sum(self.values) / len(self.values)
 
+  def empty(self):
+    return len(self.values) == 0
+
   def __str__(self):
     if self.csv:
       ret = [self.key]
@@ -179,6 +182,9 @@ def main():
     for category in categories:
       category.process_entry(obj)
 
+  # Filter out empty categories.
+  categories = [x for x in categories if not x.empty()]
+
   if args.rank != "no":
     categories = sorted(categories, key=make_key_func(args.rank), reverse=True)