Exception: Cannot call method "clear" of null. line number: 117

This error generates because the script expects the spreadsheet to have a tab with name: Keywords. If there is none, the spreadsheet will return empty, and this error message will be displayed. To fix this, you'll need to add on a tab with the name Keywords, or change the settings over to "New" to that the script will create a new spreadsheet with results each time it runs.