Add delete a baggage item in span

span_context.go

@@ -314,6 +314,7 @@ func (c *SpanContext) CopyFrom(ctx *SpanContext) {
 }
 
 // WithBaggageItem creates a new context with an extra baggage item.
+// Delete a baggage item if provided blank value.
 //
 // The SpanContext is designed to be immutable and passed by value. As such,
 // it cannot contain any locks, and should only hold immutable data, including baggage.
@@ -324,6 +325,19 @@ func (c *SpanContext) CopyFrom(ctx *SpanContext) {
 // a trace), or it needs to do a copy-on-write, which is the approach taken here.
 func (c SpanContext) WithBaggageItem(key, value string) SpanContext {
 	var newBaggage map[string]string
+	// unset baggage item
+	if value == "" {
+		if _, ok := c.baggage[key]; ok {
+			newBaggage = make(map[string]string, len(c.baggage))
+			for k, v := range c.baggage {
+				newBaggage[k] = v
+			}
+			delete(newBaggage, key)
+		} else {
+			newBaggage = c.baggage
+		}
+		return SpanContext{c.traceID, c.spanID, c.parentID, newBaggage, "", c.samplingState, c.remote}
+	}
 	if c.baggage == nil {
 		newBaggage = map[string]string{key: value}
 	} else {

span_context_test.go

@@ -79,6 +79,16 @@ func TestSpanContext_WithBaggageItem(t *testing.T) {
 	assert.Equal(t, map[string]string{"some-KEY": "Some-Other-Value"}, ctx.baggage)
 }
 
+func TestSpanContext_WithBaggageItem_Delete(t *testing.T) {
+	var ctx SpanContext
+	ctx = ctx.WithBaggageItem("some-KEY", "")
+	assert.Nil(t, ctx.baggage)
+	ctx = ctx.WithBaggageItem("some-KEY", "Some-Value")
+	assert.Equal(t, map[string]string{"some-KEY": "Some-Value"}, ctx.baggage)
+	ctx = ctx.WithBaggageItem("some-KEY", "")
+	assert.Equal(t, map[string]string{}, ctx.baggage)
+}
+
 func TestSpanContext_Flags(t *testing.T) {
 
 	var tests = map[string]struct {