Filter out classes without names in the sampler

We can't do a lot with classes without names as we can't filter by them,
have no idea where they come from, etc. As such it's best to just ignore
these.

lib/gitlab/metrics/sampler.rb

@@ -66,7 +66,11 @@ module Gitlab
         def sample_objects
           sample = Allocations.to_hash
           counts = sample.each_with_object({}) do |(klass, count), hash|
-            hash[klass.name] = count
+            name = klass.name
+
+            next unless name
+
+            hash[name] = count
           end
           # Symbols aren't allocated so we'll need to add those manually.

spec/lib/gitlab/metrics/sampler_spec.rb

@@ -72,14 +72,25 @@ describe Gitlab::Metrics::Sampler do
     end
   end
-  describe '#sample_objects' do
-    it 'adds a metric containing the amount of allocated objects' do
-      expect(sampler).to receive(:add_metric).
-        with(/object_counts/, an_instance_of(Hash), an_instance_of(Hash)).
-        at_least(:once).
-        and_call_original
-      sampler.sample_objects
+  if Gitlab::Metrics.mri?
+    describe '#sample_objects' do
+      it 'adds a metric containing the amount of allocated objects' do
+        expect(sampler).to receive(:add_metric).
+          with(/object_counts/, an_instance_of(Hash), an_instance_of(Hash)).
+          at_least(:once).
+          and_call_original
+
+        sampler.sample_objects
+      end
+      it 'ignores classes without a name' do
+        expect(Allocations).to receive(:to_hash).and_return({ Class.new => 4 })
+
+        expect(sampler).not_to receive(:add_metric).
+          with('object_counts', an_instance_of(Hash), type: nil)
+
+        sampler.sample_objects
+      end
     end
   end