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

@@ -72,6 +72,7 @@ describe Gitlab::Metrics::Sampler do
     end
   end
 
+  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).
@@ -81,6 +82,16 @@ describe Gitlab::Metrics::Sampler do
 
         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
 
   describe '#sample_gc' do