I have a scenario where I need to populate the value of a parent object on its child record which is in a master detail relationship. 

For instance, I have a Custom Object “Customer Number” which is in Master Detail relationship with Leads. Instead of pass Salesforce ID, I want to pass the Lead.Name (as it is available in Streamsets) to establish the relationship of “Customer Number” record to its parent Lead object. What is the syntax that I need to use?