Handle empty instance label in push.rb

Signed-off-by: Chris Sinjakli <chris@sinjakli.co.uk>

Author: Sinjo

lib/prometheus/client/push.rb

@@ -71,7 +71,7 @@ def parse(url)
       end
 
       def build_path(job, instance)
-        if instance
+        if instance && !instance.empty?
           format(INSTANCE_PATH, CGI::escape(job), CGI::escape(instance))
         else
           format(PATH, CGI::escape(job))

spec/prometheus/client/push_spec.rb

@@ -76,6 +76,12 @@
       expect(push.path).to eql('/metrics/job/test-job')
     end
 
+    it 'uses the default metrics path if an empty instance value is given' do
+      push = Prometheus::Client::Push.new(job: 'bar-job', instance: '')
+
+      expect(push.path).to eql('/metrics/job/bar-job')
+    end
+
     it 'uses the full metrics path if an instance value is given' do
       push = Prometheus::Client::Push.new(job: 'bar-job', instance: 'foo')