add client tracing

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

errors/errors.go

@@ -262,6 +262,10 @@ func CodeIn(err interface{}, codes ...int32) bool {
 
 // FromError try to convert go error to *Error
 func FromError(err error) *Error {
+	if err == nil {
+		return nil
+	}
+
 	if verr, ok := err.(*Error); ok && verr != nil {
 		return verr
 	}