Update Statsd tag serializer to allow falsy values

This instead now ensures that we skip including the tag value only if:
- it is equal to 'nil'
- it when stringified is equal to 'nil'

The reasoning for this was to make it so falsy values (e.g. false) will now be
included in our tag content, instead of skipped.

lib/datadog/statsd/serialization/tag_serializer.rb

@@ -59,10 +59,10 @@ def to_tags_list(tags)
           case tags
           when Hash
             tags.map do |name, value|
-              if value
-                escape_tag_content("#{name}:#{value}")
-              else
+              if value&.to_s.nil?
                 escape_tag_content(name)
+              else
+                escape_tag_content("#{name}:#{value}")
               end
             end
           when Array
@@ -75,7 +75,7 @@ def to_tags_list(tags)
         def escape_tag_content(tag)
           tag = tag.to_s
           return tag unless tag.include?('|')
-          tag.delete('|,')        
+          tag.delete('|,')
         end
 
         def dd_tags(env = ENV)

spec/statsd/serialization/tag_serializer_spec.rb

@@ -139,6 +139,20 @@
         expect(subject.format([tag])).to eq 'node:storage'
       end
 
+      it 'ignores nil values and formats all other falsy values correctly' do
+        message_tags_hash = {
+          empty_array: [],
+          missing: nil,
+          'empty_hash' => {},
+          blank: '',
+          :false_value => false,
+          'results in blank': double('some tag', to_s: ''),
+          'results in nil': double('some tag', to_s: nil),
+        }
+
+        expect(subject.format(message_tags_hash)).to eq 'empty_array:[],missing,empty_hash:{},blank:,false_value:false,results in blank:,results in nil'
+      end
+
       it 'formats frozen tags correctly' do
         expect(subject.format(['name:foobarfoo'.freeze])).to eq 'name:foobarfoo'
       end