Parameters containing equals sign have their value stripped

[Gert-dev]

It seems that if you enter a parameter containing an equals sign in the Additional command line box in the UI, the value after the equals sign and the equals sign itself are stripped. For example:

--exclude-group=SomeGroup

becomes

--exclude-group

I think this line is the culprit. It assigns a substring to arg to check if it is an allowed parameter. But if it is, it proceeds to push the stripped version, instead of the entire original version.