Problem Definition
In a Docker task, when a name/path is given under Working subdirectory under Advanced options, it does not create a new subdirectory if it does not exist already (but Source code checkout task creates a new directory if it doesn't exist).
Suggested Solution
Alter the help text from "Specify an alternative subdirectory as working directory for the task." with "Specify a pre-existing alternative subdirectory as working directory for the task." so as to avoid confusion.