html:
Having your locator based on the ng-click is not quite reliable and readable.
Instead I would rely on the button text:
by.xpath('//button[contains(., "Select None")]')
or, on the class:
by.css('button.helperButton')
Or, if have a control over the application HTML templates - add an id attribute and use:
by.id('mybuttonid')
If you still want to use ng-click - try using starts-with CSS selector syntax to check ng-click attribute:
by.css('button[ng-click^=select]')