Capybara error: undefined method `node_name’ for nil:NilClass

When trying to use click_button on a button in a form, if you get this error:

undefined method `node_name' for nil:NilClass

Check that the button is inside a form. As in, the following code will cause this error:

HTML:

<form></form>
<input type="submit" value="save" />

Capybara:

click_button "save"

Moving the button to the inside of the form will fix the issue.