Android Studio's UI was just hiding the error...
when the error occurred, it highlighted the item in the list view, and showed an unhelpful message in the terminal view. [![unhelpful error message appears when erroneous item is selected][1]][1]
to find the real error, select the root item in the list view so that Android Studio would display the whole build output in the terminal view, then scroll to find error. [![helpful error message appars when you select the root item from the list view on the left][2]][2]
[1]: https://i.stack.imgur.com/3cibL.png [2]: https://i.stack.imgur.com/tpXmd.png

Android Studio's UI was just hiding the error...
when the error occurred, it highlighted the item in the list view, and showed an unhelpful message in the terminal view. [![bad bad][1]][1]
to find the real error, select the root item in the list view so that Android Studio would display the whole build output in the terminal view, then scroll to find error. [![good good][2]][2]

[1]: https://i.stack.imgur.com/fEShu.png [2]: https://i.stack.imgur.com/eWduo.png