"invalid value / unknown config name: dm1" when give empty tls config

[D3Hunter]

What did you do?

• start job with target config:

target-database:
  host: aaxxxxx
  port: 4000
  user: root
  password: "123456"
  max-allowed-packet: null
  session: {}
  security:
    ssl-ca: ""
    ssl-cert: ""
    ssl-key: ""
    cert-allowed-cn: []
    ssl-ca-bytes: []
    ssl-key-bytes: []
    ssl-cert-bytes: []
    ssl-ca-base64: ""
    ssl-key-base64: ""
    ssl-cert-base64: ""

• job fail with "invalid value / unknown config name: dm1"

caused by this line, it returns nil, nil on empty tls

tiflow/dm/pkg/conn/basedb.go

Line 71 in e8961d8

tlsConfig, err := util.NewTLSConfig(

What did you expect to see?

skip tls cert or report tls cert error

What did you see instead?

empty config

Versions of the cluster

current master branch

current status of DM cluster (execute query-status <task-name> in dmctl)

(paste current status of DM cluster here)

[D3Hunter]

@liumengya94 ptal

/cc @lance6716