Handle nil tag values gracefully in CompiledMetric

- Use %s placeholder for all tag types (instead of %d/%f) for uniform handling
- Sanitize string and symbol values only (sprintf handles conversion for other types)
- nil values are handled gracefully (converted to empty string by sprintf)

Author: kelhusseiny

CHANGELOG.md

@@ -6,6 +6,7 @@ section below.
 
 ## Unreleased changes
 
+- Add support for `nil` tag values in `CompiledMetric` dynamic tags (converted to empty string).
 - [#407](https://github.com/Shopify/statsd-instrument/pull/407) - Add support for `Symbol` and `:Boolean` types in `CompiledMetric` dynamic tags, allowing symbol and boolean values to be used as tag values.
 - [#403](https://github.com/Shopify/statsd-instrument/pull/403) - Add `CompiledMetric::Distribution` as the second metric type to support pre-compiled metric datagrams. It can be used as a replacement over standard `StatsD.distribution`.
 - [#404](https://github.com/Shopify/statsd-instrument/pull/404) - Fix bug when using aggregation; finalizer was called with the wrong values.

lib/statsd/instrument/compiled_metric.rb

@@ -323,22 +323,11 @@ def compile_static_tags(static_tags)
           def compile_dynamic_tags(dynamic_tags)
             dynamic_tags.map do |key, type|
               tag_name = normalize_statsd_string(key)
-              placeholder =
-                if type == String
-                  "%s"
-                elsif type == Integer
-                  "%d"
-                elsif type == Float
-                  "%f"
-                elsif type == :Boolean
-                  "%s"
-                elsif type == Symbol
-                  "%s"
-                else
-                  raise ArgumentError,
-                    "Unsupported tag value type: #{type}. Use String, Integer, Float, Symbol, or :Boolean."
-                end
-              "#{tag_name}:#{placeholder}"
+              unless [String, Integer, Float, Symbol, :Boolean].include?(type)
+                raise ArgumentError,
+                  "Unsupported tag value type: #{type}. Use String, Integer, Float, Symbol, or :Boolean."
+              end
+              "#{tag_name}:%s"
             end
           end
         end
@@ -371,7 +360,7 @@ def to_datagram(value)
           # Fast path: no tag values (static metrics)
           return @datagram_blueprint % packed_value if @tag_values.empty?
 
-          # Sanitize string and symbol values
+          # Sanitize string and symbol values (other types handled by sprintf %s)
           values = @tag_values.map do |arg|
             if arg.is_a?(String)
               /[|,]/.match?(arg) ? arg.tr("|,", "") : arg

test/compiled_metric_test.rb

@@ -224,6 +224,20 @@ def test_sanitizes_symbol_dynamic_tag_values
     assert_equal(["status:activewithspecial"], @sink.datagrams.first.tags)
   end
 
+  def test_handles_nil_tag_values
+    metric = Class.new(StatsD::Instrument::CompiledMetric::Counter) do
+      define(
+        name: "foo.bar",
+        tags: { shop_id: Integer, name: String, rate: Float },
+      )
+    end
+
+    metric.increment(1, shop_id: nil, name: nil, rate: nil)
+
+    assert_equal(1, @sink.datagrams.size)
+    assert_equal(["name:", "rate:", "shop_id:"], @sink.datagrams.first.tags.sort)
+  end
+
   def test_emits_metric_when_cache_exceeded
     # Create a metric with a very small cache size
     metric = Class.new(StatsD::Instrument::CompiledMetric::Counter) do