Dropdown: onMouseDown should be given undefined, not false, when disabled

Warning: Expected `onMouseDown` listener to be a function, instead got `false`.

If you used to conditionally omit it with onMouseDown={condition && value}, pass onMouseDown={condition ? value : undefined} instead.

import Dropdown from 'react-toolbox/lib/dropdown/Dropdown';

...

let newLocationOptions = [{
  value: "initial", label: "Select a Location", disabled: true
},{
  value: "add-new-location", label: "Add New Location"
},{
  value: "empty", label: "Your Locations:", disabled: true
}]

...

<Dropdown
  key={selectedLocation}
  auto={false}
  label="Event Location"
  onChange={this.locationChangeHandler}
  source={newLocationOptions}
  value={selectedLocation}
  required={true}
/>

onMouseDown={!item.disabled && this.handleSelect.bind(this, item[valueKey])}

onMouseDown={item.disabled ? undefined : this.handleSelect.bind(this, item[valueKey])}