Merge pull request #10455 from wjwithagen/wip-wjw-clang-NULL

src/kv/MemDB.cc: the type of the parameter of push_back() does not match the ops's value_type

Reviewed-by: Ramesh Chander <Ramesh.Chander@sandisk.com>
Reviewed-by: Kefu Chai <kchai@redhat.com>

src/kv/MemDB.cc

@@ -231,7 +231,7 @@ void MemDB::MDBTransactionImpl::rmkey(const string &prefix,
   dtrace << __func__ << " " << prefix << " " << k << dendl;
   ops.push_back(make_pair(DELETE,
                           std::make_pair(std::make_pair(prefix, k),
-                          NULL)));
+                          bufferlist())));
 }
 
 void MemDB::MDBTransactionImpl::rmkeys_by_prefix(const string &prefix)