Event target is null inside functional setState

Question

Consider below function of some component:

handleInputChange(e) {
    // let val = e.target.value; - if I uncomment this, it works.

    // Update text box value
    this.setState(function (prevState, props) {
        return {
          searchValue: e.target.value,
        }
    })
}

and a textbox, which is rendered by a child component of above component, and receives handleInputChange as props:

<input type="text" onChange={that.props.handleInputChange} value={that.props.searchValue} />

When I enter something in text field I get error that Cannot read property 'value' of null.

If I uncomment the first line inside handleInputChange function, where I store text box value inside val variable, it works well. Ideas why?