Assertion when trying to capture React Modal Portal

[RonAtConduce]

pass in a react modal portal div with the --selector option and the program crashes.
e.g. webkit2pgn -F --selector="div.

2018-01-31 10:06:34.921 Python[27092:1927977] *** Assertion failure in -[NSBitmapImageRep initWithCGImage:], /SourceCache/AppKit/AppKit-1348.17/AppKit.subproj/NSBitmapImageRep.m:1288
/usr/local/bin/webkit2png:259: UninitializedDeallocWarning: leaking an uninitialized object of type NSBitmapImageRep
bitmapdata = AppKit.NSBitmapImageRep.alloc().initWithCGImage_(cropped)
2018-01-31 10:06:34.923 Python[27092:1927977] Invalid parameter not satisfying: cgImage != NULL
2018-01-31 10:06:34.924 Python[27092:1927977] (
0 CoreFoundation 0x00007fff91e9203c __exceptionPreprocess + 172
1 libobjc.A.dylib 0x00007fff8f1e676e objc_exception_throw + 43
2 CoreFoundation 0x00007fff91e91bd9 -[NSException raise] + 9
3 _objc.so 0x0000000109924a8b PyObjCErr_ToObjCWithGILState + 46
4 _objc.so 0x000000010991152d PyObjCFFI_MakeClosure + 5097
5 libffi.dylib 0x00007fff8d498a07 ffi_closure_unix64_inner + 511
6 libffi.dylib 0x00007fff8d4980c6 ffi_closure_unix64 + 70
7 CoreFoundation 0x00007fff91de5204 CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION + 20
8 CoreFoundation 0x00007fff91de4e93 __CFRunLoopDoTimer + 1059
9 CoreFoundation 0x00007fff91e5853d __CFRunLoopDoTimers + 301
10 CoreFoundation 0x00007fff91da0428 __CFRunLoopRun + 2024
11 CoreFoundation 0x00007fff91d9f9f8 CFRunLoopRunSpecific + 296
12 HIToolbox 0x00007fff98a0256f RunCurrentEventLoopInMode + 235
13 HIToolbox 0x00007fff98a022ea ReceiveNextEventCommon + 431
14 HIToolbox 0x00007fff98a0212b _BlockUntilNextEventMatchingListInModeWithFilter + 71
15 AppKit 0x00007fff8c1668ab _DPSNextEvent + 978
16 AppKit 0x00007fff8c165e58 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 346
17 AppKit 0x00007fff8c15baf3 -[NSApplication run] + 594
18 libffi.dylib 0x00007fff8d497f44 ffi_call_unix64 + 76
19 ??? 0x00007fe150cae580 0x0 + 140605699843456
)

[paulhammond]

I'm struggling to reproduce this. Can you provide an example URL (or even a react app I can run locally on my laptop) that will trigger it?