fix bug that tag form:",default=1" are not effective in some cases, e.g: http://host/list?page_no=&page_size=

binding/form_mapping.go

@@ -163,8 +163,10 @@ func setByForm(value reflect.Value, field reflect.StructField, form map[string][
 			val = opt.defaultValue
 		}
 
-		if len(vs) > 0 {
+		if len(vs) > 0 && vs[0] != "" {
 			val = vs[0]
+		} else {
+			val = opt.defaultValue
 		}
 		return true, setWithProperType(val, value, field)
 	}