Hello,

Thanks again for your last bugfix. Here is another issue:

./bin/blast-index start --node-id=index1 --data-dir=/tmp/blast/index1 --bind-addr=:6060 --grpc-addr=:5050 --http-addr=:8080 --index-mapping-file ./example/index_mapping.json
2019/03/14 16:26:27.068886 github.com/mosuka/blast/index/server.go:131 [ERR] listen tcp :8080: bind: address already in use
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x48 pc=0xb51108]

goroutine 39 [running]:
github.com/mosuka/blast/index.(*Server).Start(0x0)
/home/rbastic/go-src/src/github.com/mosuka/blast/index/server.go:147 +0x68
created by main.execStart
/home/rbastic/go-src/src/github.com/mosuka/blast/cmd/blast-index/start.go:78 +0x802