> be fist commit

internal/xlerrors/notfound.go

@@ -0,0 +1,18 @@
+package xlerrors
+
+type notFoundError struct {
+	Subject string
+}
+
+func (err *notFoundError) Error() string {
+	return err.Subject + " not found"
+}
+
+func NotFound(subject string) error {
+	return &notFoundError{Subject: subject}
+}
+
+func IsNotFound(err error) bool {
+	_, ok := err.(*notFoundError)
+	return ok
+}