You can specify a blank default value by using the format for a default value but not enter anything after the equals sign. Ex:
{
"parameterName": "${VARIABLE_NAME=}"
}
In the User-Defined Overrides section you can elect to use the default value by deleting whatever is currently in the text field. There is currently a bug that prevents you from saving if the default value is blank. I have escalated this issue in our bug tracker so it will be fixed sooner. Un-setting the device value to use the default works if a non-blank default is used.
As a temporary work around you could use a space character if you are using cnPilot Home. This would allow you to save without entering a device-specific value and an extra space shouldn't typically change the CLI script.
{
"parameterName": "${VARIABLE_NAME= }"
}
Is this for a cnPilot Home device? The below Knowledge Base article lists a procedure for detemining what configuration fields to use regardless of device type.
We currently don't sort user-defined overrides at all but we also don't do anything to preserve the ordering for displaying them in the UI.