Need to provide default values for derived output parameters in ArcGIS tools

[jjr8]

Without default values, the output parameter oval remains white in the geoprocessing modeler, which prevents subsequent tools from running. It means we have to provide a default value for all parameters (I think) if we want models to run to completion in one execution cycle. If we don't provide default values, I think you have to run them one step at a time, with each step unlocking the next one as a value is provided for the derived output parameter on the tool that was last executed.

Fixed in [14].