Calendar throws exception when have the onViewDateChange property

[xenouk]

Hi, I cannot use Calendar with the onViewDateChange property. An exception is immediately thrown.

[x] bug report

Current behavior
TypeError: Cannot read property 'getMonth' of null
Calendar.renderDateView
C:/Dev/RE_Project/Frontier-Risk-Web/node_modules/primereact/calendar/calendar.esm.js:3124
3121 | key: "renderDateView",
3122 | value: function renderDateView() {
3123 | var viewDate = this.getViewDate();

3124 | var monthsMetaData = this.createMonths(viewDate.getMonth(), viewDate.getFullYear());
| ^ 3125 | var months = this.renderMonths(monthsMetaData);
3126 | return /#PURE/React.createElement(React.Fragment, null, months);
3127 | }

Expected behavior
No Exception

Minimal reproduction of the problem with instructions
<Calendar onViewDateChange={() => {}} />

• React version:
  v16.13.1

• PrimeReact version:
  v6.5.1

• Browser: [Chrome]

• Language: [all]