Could not find method exteplugins() for arguments

EDIT: This is now a bug report. Seeing the documentation, the method is clearly supposed to be 'plugins'. My file was generated with 'exteplugins' for some reason.

I'm following this Getting Started guide for writing plugins, with the goal of writing a PHPStorm plugin. However, when I get to the end of the guide and double-click 'runIde', I get this error:

Could not find method exteplugins() for arguments [build_4kia8bvxf9r8rsv5nosykoc6t$_run_closure1@568a0855] on root project 'test-reporting' of type org.gradle.api.Project.

I tried Googling the method exteplugins (in quotes, because Google was suggesting plenty of other search terms), and Google literally comes up with no results. What on earth? This method, that is on line 1 of the build file, does not appear anywhere on the internet? No documentation whatsoever? Nothing?

How do I solve this?