update:SetMode function (#2321)

mode.go

@@ -50,8 +50,12 @@ func init() {
 
 // SetMode sets gin mode according to input string.
 func SetMode(value string) {
+	if value == "" {
+		value = DebugMode
+	}
+
 	switch value {
-	case DebugMode, "":
+	case DebugMode:
 		ginMode = debugCode
 	case ReleaseMode:
 		ginMode = releaseCode
@@ -60,9 +64,7 @@ func SetMode(value string) {
 	default:
 		panic("gin mode unknown: " + value)
 	}
-	if value == "" {
-		value = DebugMode
-	}
+
 	modeName = value
 }