array of  QueryParam problem

if I wan to parse a query param  to  string[] . for example:
```bash
GET /xxx?p=xx&p=yy
```
with router:  
```typescript
@Get('/xxx')
fun(@QueryParam('flags') flags: string[]){
}
```
will be ok, bug When 
```bash
GET /xxx?p=xx
```
will cause an error:
```
Given parameter p is invalid. Value (\"a\") cannot be parsed into JSON.
```
