[GitHub] [dubbo] seedeed commented on issue #5768: fix a potential NPE in CallbackServiceCodec.java

["seedeed (GitHub)" <gi...@apache.org>]

I'm not sure whether the url is always not null. But I found that there already exists a null check for the url before setting the variable named group in this method. So I thought one more null check for this url is still needed before calling its getParameters method anyway.

```java
    /**
     * export or unexport callback service on client side
     *
     * @param channel
     * @param url
     * @param clazz
     * @param inst
     * @param export
     * @throws IOException
     */
    @SuppressWarnings({"unchecked", "rawtypes"})
    private static String exportOrUnexportCallbackService(Channel channel, URL url, Class clazz, Object inst, Boolean export) throws IOException {
        int instid = System.identityHashCode(inst);
        Map<String, String> params = new HashMap<>(3);
        // no need to new client again
        params.put(IS_SERVER_KEY, Boolean.FALSE.toString());
        // mark it's a callback, for troubleshooting
        params.put(IS_CALLBACK_SERVICE, Boolean.TRUE.toString());
        String group = (url == null ? null : url.getParameter(GROUP_KEY));
        if (group != null && group.length() > 0) {
            params.put(GROUP_KEY, group);
        }
        // add method, for verifying against method, automatic fallback (see dubbo protocol)
        params.put(METHODS_KEY, StringUtils.join(Wrapper.getWrapper(clazz).getDeclaredMethodNames(), ","));

        Map<String, String> tmpMap = new HashMap<>(url.getParameters());
```

[ Full content available at: https://github.com/apache/dubbo/pull/5768 ]
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