grpc: error while marshaling: proto: Marshal called with nil when creating a table that already exists in jupyter notebook

[typhoonzero]

Start sqlflowserver in the Docker container by ./sqlflowserver &, then run SQL statement

create table mytable as select ...;

if mytable is already exists, the below error is reported.

_MultiThreadedRendezvous: <_MultiThreadedRendezvous of RPC that terminated with:
	status = StatusCode.INTERNAL
	details = "grpc: error while marshaling: proto: Marshal called with nil"
	debug_error_string = "{"created":"@1602661393.999438200","description":"Error received from peer ipv4:127.0.0.1:50051","file":"src/core/lib/surface/call.cc","file_line":1061,"grpc_message":"grpc: error while marshaling: proto: Marshal called with nil","grpc_status":13}"