Missing space prefix when header class is function

[LeoVie]

This template code

<ngx-datatable-column name="name" [headerClass]="getHeaderClass" />

with

protected getHeaderClass() {
  return 'foo';
}

produces this result:

<datatable-header-cell role="columnheader" resizeable="" long-press="" draggable="" class="datatable-header-cell resizeablefoo sortable resizeable" ...>

There is a space missing between resizable and foo.

This only occurs when passing a function to [headerClass], that returns a string. Passing a string directly to the property as well as passing a function, that returns an object, does not lead to the error.

The issue lays in the header-cell.component.ts in get columnCssClasses:

if (this.column.headerClass) {
  if (typeof this.column.headerClass === 'string') {
    cls += ' ' + this.column.headerClass;
  } else if (typeof this.column.headerClass === 'function') {
    const res = this.column.headerClass({
      column: this.column
    });

    if (typeof res === 'string') {
      cls += res; // <-- Here is the error, this must be cls += ' ' + res
    } else if (typeof res === 'object') {
      const keys = Object.keys(res);
      for (const k of keys) {
        if (res[k] === true) {
          cls += ` ${k}`;
        }
      }
    }
  }
}