Fix some NULL usage

include/grpc++/resource_quota.h

@@ -37,6 +37,7 @@
 struct grpc_resource_quota;
 
 #include <grpc++/impl/codegen/config.h>
+#include <grpc++/impl/codegen/grpc_library.h>
 
 namespace grpc {
 
@@ -44,7 +45,7 @@ namespace grpc {
 /// A ResourceQuota can be attached to a server (via ServerBuilder), or a client
 /// channel (via ChannelArguments). gRPC will attempt to keep memory used by
 /// all attached entities below the ResourceQuota bound.
-class ResourceQuota final {
+class ResourceQuota final : private GrpcLibraryCodegen {
  public:
   explicit ResourceQuota(const grpc::string& name);
   ResourceQuota();

src/core/lib/iomgr/ev_epoll_linux.c

@@ -830,7 +830,8 @@ static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
 
 static grpc_closure_scheduler *workqueue_scheduler(grpc_workqueue *workqueue) {
   polling_island *pi = (polling_island *)workqueue;
-  return &pi->workqueue_scheduler;
+  return workqueue == NULL ? grpc_schedule_on_exec_ctx
+                           : &pi->workqueue_scheduler;
 }
 
 static grpc_error *polling_island_global_init() {