QtCoAP build failure in '5.15'

agent:2019/11/06 05:51:08 build.go:220: cd simplecoapclient/ && ( test -e Makefile || /home/qt/work/install/bin/qmake -o Makefile /home/qt/work/qt/qtcoap/examples/coap/simplecoapclient/simplecoapclient.pro INSTALL_PREFIX=/home/qt/work/install ) && make -f Makefile
agent:2019/11/06 05:51:08 build.go:220: Project ERROR: Unknown module(s) in QT: widgets
agent:2019/11/06 05:51:08 build.go:220: Makefile:72: recipe for target 'sub-simplecoapclient-make_first' failed
agent:2019/11/06 05:51:08 build.go:220: make[2]: *** [sub-simplecoapclient-make_first] Error 3
agent:2019/11/06 05:51:08 build.go:220: make[2]: *** Waiting for unfinished jobs....

Build log: https://testresults.qt.io/logs/qt/qtcoap/cc32de2081743a8970c892d6778eb46acda07880/LinuxUbuntu_18_04x86_64LinuxUbuntu_18_04x86_64GCCqtci-linux-Ubuntu-18.04-x86_64-d00b90/d9d2bd79727bb4023cf1ea06e536f94d6c777ef5/build_1573019189/log.txt.gz

Details: http://ci-files01-hki.intra.qt.io:8080/coin/integration/qt/tqtc-qt5/tasks/1573018527
Tested changes (refs/builds/qtci/tqtc/5.15/1573018527):
https://codereview.qt-project.org/c/qt/tqtc-qt5/+/280484 Merge remote-tracking branch 'origin/5.15' into tqtc/5.15