optimise when bVals is empty as suggested -- also add test case for empty bVals

Author: jamesmoessis

propagation/baggage.go

@@ -56,6 +56,9 @@ func extractSingleBaggage(parent context.Context, carrier TextMapCarrier) contex
 
 func extractMultiBaggage(parent context.Context, carrier MultiTextMapCarrier) context.Context {
 	bVals := carrier.Values(baggageHeader)
+	if len(bVals) == 0 {
+		return parent
+	}
 	members := make([]baggage.Member, 0)
 	for _, bStr := range bVals {
 		currBag, err := baggage.Parse(bStr)

propagation/baggage_test.go

@@ -162,6 +162,11 @@ func TestExtractValidMultipleBaggageHeaders(t *testing.T) {
 			headers: []string{"", ""},
 			want:    members{},
 		},
+		{
+			name:    "none",
+			headers: []string{},
+			want:    members{},
+		},
 	}
 
 	for _, tt := range tests {