apollo-portal/src/main/java/com/ctrip/framework/apollo/openapi/v1/controller/NamespaceBranchController.java/NamespaceBranchController/getBranchGrayRules
class NamespaceBranchController:    @GetMapping(value = "/apps/{appId}/clusters/{clusterName}/namespaces/{namespaceName}/branches/{branchName}/rules")
    public OpenGrayReleaseRuleDTO getBranchGrayRules(@PathVariable String appId, @PathVariable String env,
                                                     @PathVariable String clusterName,
                                                     @PathVariable String namespaceName,
                                                     @PathVariable String branchName) {
        GrayReleaseRuleDTO grayReleaseRuleDTO = namespaceBranchService.findBranchGrayRules(appId, Env.valueOf(env.toUpperCase()), clusterName, namespaceName, branchName);
        if (grayReleaseRuleDTO == null) {
            return null;
        }
        return OpenApiBeanUtils.transformFromGrayReleaseRuleDTO(grayReleaseRuleDTO);
    }