When the package is downloaded from Orchestrator and uploaded to studio for enhancement and then publish back the newer version back to Orchestrator then error might throw " [Error: System.NullReferenceException: Object reference not set to an instance of an object]
Root Cause: Check any files/Folders in your process flow have %20 as this will be automatically created wherever “space” is present in files/folders of your process. This will occur when the package is downloaded and extracted the process files.
Solution: Rename the folder/files which are have %20 without space OR use “_”(underscore) instead of spaces between the file/Folder names.
And then publish again so that issue will be solved.
Also the coding standard to be followed on naming file/folders should be no spaces between the words.