Workspace.get_targets() returns None for targets where no default Target class is specified

[guenp]

Problem: If no default target is specified, Workspace.get_targets() returns None and throws a confusing warning message.
The reason why no Target is returned is because we don't have the following parameters that are required for the Target constructor:

provider_id: str = "",
input_data_format: str = "",
output_data_format: str = "",
content_type: str = "",
encoding: str = "",

Without this information a Target instance cannot be used to submit a Job.

Proposed solution: If no default target is specified, return a Target instance that will fail if you call .submit().

Thanks @xinyi-joffre for catching this.

[guenp]

Other issues: the link returned in the warning has a dot in it that results in a broken link when used from a Jupyter notebook.