docs dont indicate that a default property needs to be defined for results

Description of problem:  docs don't indicate that a default property needs to be defined for results

Prerequisites (if any, like setup, operators/versions):

Steps to Reproduce

1.  Do a task run with no default property defined for results and the task run fails. This is not captured in the documentation.

Actual results:

Docs dont have any info on the need to define a default property for results

Expected results:

Docs should contain info{}

Reproducibility (Always/Intermittent/Only Once):

Build Details:

Additional info (Such as Logs, Screenshots, etc):