Internal Error

MessageNotUnderstood: receiver of "configAt:default:" is nil

[] in WBBookingSession>>bookingPage
[] in Dictionary>>at:ifAbsentPut:
Dictionary>>at:ifAbsent:
Dictionary>>at:ifAbsentPut:
[] in SSharedDictionary>>at:ifAbsentPut:
[] in Monitor>>critical:
BlockClosure>>ensure:
Monitor>>critical:
SSharedDictionary>>at:ifAbsentPut:
WBBookingSession(SSSession)>>at:ifAbsentPut:
WBBookingSession>>bookingPage
WBBookingSession>>updateRoot:
WBRenderContinuation(WASessionContinuation)>>updateRoot:
WBRenderContinuation>>updateRoot:
WBRenderContinuation>>newHtmlRoot
WBRenderContinuation(WARenderContinuation)>>processRendering:
[] in WBRenderContinuation(WARenderContinuation)>>render
WBRenderContinuation(WASessionContinuation)>>respond:
WBRenderContinuation(WARenderContinuation)>>render
[] in WBRenderContinuation(WARenderContinuation)>>run