bluepill: Terminating app due to uncaught exception

Running this:

bluepill -a XXXX.app/ -s XXXX.xcscheme -o output/

crashes and returns this:

bluepill[78419:3224648] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSSingleObjectArrayI objectAtIndex:]: index 1 beyond bounds [0 .. 0]'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff7d8390db __exceptionPreprocess + 171
	1   libobjc.A.dylib                     0x00007fff924cba2a objc_exception_throw + 48
	2   CoreFoundation                      0x00007fff7d8a3b4f -[__NSSingleObjectArrayI objectAtIndex:] + 111
	3   bluepill                            0x000000010bb80448 +[BPXCTestFile BPXCTestFileFromExecutable:withError:] + 872
	4   bluepill                            0x000000010bb7f746 +[BPApp BPAppWithAppBundlePath:withExtraTestBundles:withError:] + 907
	5   bluepill                            0x000000010bb78b3c main + 739
	6   libdyld.dylib                       0x00007fff92dad255 start + 1
	7   ???                                 0x0000000000000007 0x0 + 7
)
libc++abi.dylib: terminating with uncaught exception of type NSException
Abort trap: 6