Clear button in daily planning doesn't work

Pressing clear button results removing all elements from calendar, but nothing is added to the top panel. Moreover save doesn't persist cleared data and there is an error in the JS console:

Uncaught TypeError: Cannot read property 'substring' of undefined
    at remove_event (daily_planning.7106c7605db6.js:242)
    at Object.<anonymous> (daily_planning.7106c7605db6.js:353)
    at Function.each (jquery-2.2.3.min.33cabfa15c10.js:2)
    at HTMLButtonElement.click (daily_planning.7106c7605db6.js:352)
    at h (fullcalendar.min.bc315925a4d1.js:6)
    at HTMLButtonElement.<anonymous> (fullcalendar.min.bc315925a4d1.js:6)
    at HTMLButtonElement.dispatch (jquery-2.2.3.min.33cabfa15c10.js:3)
    at HTMLButtonElement.r.handle (jquery-2.2.3.min.33cabfa15c10.js:3)