react-big-calendar: Cannot read property '0' of undefined

Problem

Attempted to implement react-calendar and the back and next buttons (to change dates) are throwing this error:

Uncaught TypeError: Cannot read property '0' of undefined

It WAS previously working and I haven't changed anything within my code, so I'm quite confused.

Question

Why am I unable to use the next and back buttons (to change dates) on react-big-calendar?

Code:

import React, {Component} from 'react';
import BigCalendar from 'react-big-calendar';
import moment from 'moment';

// Setup the localizer by providing the moment (or globalize) Object
// to the correct localizer.
BigCalendar.momentLocalizer(moment); // or globalizeLocalizer

export default class CalendarComponent extends Component {

    constructor(props){
        super(props);

        this.state = {
            events: []
        }

    }

    render(){
        return (
            <div style={{flex: 1}}>
                <BigCalendar
                    events={this.state.events}
                    startAccessor='startDate'
                    endAccessor='endDate'
                />
            </div>
        );
    }
}

Library error line:

It seems to be failing at this line within the library:

MonthView.prototype.renderHeaders = function renderHeaders(row, format, culture) {
    //failes here.
    var first = row[0];
    var last = row[row.length - 1];
    var HeaderComponent = this.props.components.header || _Header2.default;

    return _dates2.default.range(first, last, 'day').map(function (day, idx) {
      return _react2.default.createElement(
        'div',
        { key: 'header_' + idx, className: 'rbc-header' },
        _react2.default.createElement(HeaderComponent, {
          date: day,
          label: _localizer2.default.format(day, format, culture),
          localizer: _localizer2.default,
          format: format,
          culture: culture
        })
      );
    });
  };