fix: empty decision maker causes errors

ddtrace/tracer/payload_test.go

@@ -174,6 +174,32 @@ func TestPayloadV1Decode(t *testing.T) {
 			assert.Equal(p.chunks[0].spans[0].spanID, got.chunks[0].spans[0].spanID)
 			assert.Equal(got.chunks[0].attributes["service"].value, "golden")
 		})
+
+		// Test that a span with no decision maker does not error
+		t.Run("no decision maker", func(t *testing.T) {
+			var (
+				assert = assert.New(t)
+				p      = newPayloadV1()
+			)
+
+			s := newBasicSpan("span.list")
+			s.context.trace.propagatingTags = map[string]string{"keyDecisionMaker": ""}
+			p.push([]*Span{s})
+			encoded, err := io.ReadAll(p)
+			assert.NoError(err)
+
+			got := newPayloadV1()
+			buf := bytes.NewBuffer(encoded)
+			_, err = buf.WriteTo(got)
+			assert.NoError(err)
+
+			o, err := got.decodeBuffer()
+			assert.NoError(err)
+			assert.Empty(o)
+			assert.Greater(len(got.chunks), 0)
+			assert.Equal(p.chunks[0].traceID, got.chunks[0].traceID)
+			assert.Equal(p.chunks[0].spans[0].spanID, got.chunks[0].spans[0].spanID)
+		})
 	}
 }
 

ddtrace/tracer/payload_v1.go

@@ -118,18 +118,33 @@ func (p *payloadV1) push(t spanList) (stats payloadStats, err error) {
 		if span == nil {
 			continue
 		}
+
+		if span.Context() == nil {
+			continue
+		}
+
 		// If we haven't seen the service yet, we set it blindly assuming that all the spans created by
 		// a service must share the same value.
 		if _, ok := attr["service"]; !ok {
 			attr["service"] = anyValue{valueType: StringValueType, value: span.Root().service}
 		}
+
 		binary.BigEndian.PutUint64(traceID[:8], span.Context().traceID.Upper())
 		binary.BigEndian.PutUint64(traceID[8:], span.Context().traceID.Lower())
 
-		if prio, ok := span.Context().SamplingPriority(); ok {
-			origin = span.Context().origin // TODO(darccio): are we sure that origin will be shared across all the spans in the chunk?
-			priority = prio                // TODO(darccio): the same goes for priority.
-			dm := span.context.trace.propagatingTag(keyDecisionMaker)
+		if span.context.trace == nil {
+			continue
+		}
+
+		// TODO(darccio): are we sure that priority will be shared across all the spans in the chunk?
+		if prio, ok := span.context.trace.samplingPriority(); ok {
+			priority = prio
+		}
+
+		// TODO(darccio): are we sure that origin will be shared across all the spans in the chunk?
+		origin = span.Context().origin
+
+		if dm := span.context.trace.propagatingTag(keyDecisionMaker); dm != "" {
 			if v, err := strconv.ParseInt(dm, 10, 32); err == nil {
 				if v < 0 {
 					v = -v