Fix bug in error reporting when adding duplicate properties

Bug: 150451422
Test: m nothing
Change-Id: Ia557992d71537aca0757866e9114b30bdf52bb6b
diff --git a/sdk/bp.go b/sdk/bp.go
index c2a75e4..68fe7ab 100644
--- a/sdk/bp.go
+++ b/sdk/bp.go
@@ -35,7 +35,7 @@
 
 func (s *bpPropertySet) AddProperty(name string, value interface{}) {
 	if s.properties[name] != nil {
-		panic("Property %q already exists in property set")
+		panic(fmt.Sprintf("Property %q already exists in property set", name))
 	}
 
 	s.properties[name] = value