启动工作流失败，显示[VAR_27026 Error: Missing initial value for session parameter:[$DBConnection_rel_gp_dcpc_ods_scada].]

这个参数连接是在会话中给目标添加连接中使用的，我之前在连接中配置了一个，但是那个可以选择类型里面有一个Greenplun Connection,但是我在会话中给目标添加连接的时候就没有这个类型了，我就写了一个参数[$DBConnection_rel_gp_dcpc_ods_scada]但是好像不太行，这个是为什么呢

具体的一个执行错误是这样的

Link [启动 --> tast]: empty expression string, evaluated to TRUE.Session task instance [tast] is waiting to be started.Session task instance [tast]: started a process with pid [15794] on node [node02].Session task instance [tast]: Execution started.Session task instance [tast] : [TM_6793 Fetching initialization properties from the Integration Service. : (Wed Nov 02 10:56:36 2022)]Session task instance [tast] : [DISP_20305 The [Preparer] DTM with process id [15794] is running on node [node02].

Session task instance [tast] : [PETL_24036 Beginning the prepare phase for the session.]Session task instance [tast] : [TM_6721 Started [Connect to Repository].]Session task instance [tast] : [TM_6722 Finished [Connect to Repository]. It took [0.38672] seconds.]Session task instance [tast] : [TM_6794 Connected to repository [REP_DCPC_BI_CLOUD_UAT] in domain [Domain_crcloudbipuat] as user [DCPC_ETLtest] in security domain [Native].]Session task instance [tast] : [TM_6721 Started [Fetch Session from Repository].]Session task instance [tast] : [TM_6722 Finished [Fetch Session from Repository]. It took [0.130239] seconds.]Session task instance [tast] : [CMN_1761 Timestamp Event: [Wed Nov 02 10:56:37 2022]]Session task instance [tast] : [VAR_27026 Error: Missing initial value for session parameter:[$DBConnection_rel_gp_dcpc_ods_scada].]Session task instance [tast] : [CMN_1761 Timestamp Event: [Wed Nov 02 10:56:37 2022]]Session task instance [tast] : [TM_6270 Error: Variable parameter expansion error.]Session task instance [tast] : [CMN_1761 Timestamp Event: [Wed Nov 02 10:56:37 2022]]Session task instance [tast] : [TM_6163 An error occurred initializing variables and parameters for the partition.]Session task instance [tast]: Execution failed.Workflow [wf_project]: Execution succeeded.