Empty strings don't work in Dropdown filters

[patorjk]

In my data there can be fields with empty strings. I noticed that the dropdown filtering doesn't work for them - it treats them the same as the "All" keyword, which leads to odd results when selecting them. You can see it in action here:

https://codesandbox.io/s/muidatatables-custom-toolbar-sisef

The problem stems from the handleDropdownChange method in TableFilter.js:

  handleDropdownChange = (event, index, column) => {
    const labelFilterAll = this.props.options.textLabels.filter.all;
    const value = event.target.value === labelFilterAll ? '' : event.target.value;
    this.props.onFilterUpdate(index, value, column, 'dropdown');
  };

It treats an empty string as well as the "All" keyword as the same, and then passes an empty string to the onFilterUpdate method (filterUpdate in MUIDataTable.js). filterUpdate hits the "default" in the switch statement for dropdowns and removes the filters on an empty string:

  filterUpdate = (index, value, column, type) => {
        ...
        switch (type) {
          case 'checkbox':
            filterPos >= 0 ? filterList[index].splice(filterPos, 1) : filterList[index].push(value);
            break;
          case 'multiselect':
            filterList[index] = value === '' ? [] : value;
            break;
          case 'custom':
            filterList[index] = value;
            break;
          default:
            filterList[index] = filterPos >= 0 || value === '' ? [] : [value];
        }

Expected Behavior

Empty strings should be valid filter options.

Current Behavior

Empty strings, as well as the All keyword, are treated the same.

Steps to Reproduce (for bugs)

1. https://codesandbox.io/s/muidatatables-custom-toolbar-sisef
2. Select the Filter icon
3. Select the empty string option

Your Environment

Tech	Version
Material-UI	2.9.0
MUI-datatables	3
React	16.4
browser	Chrome

[gabrielliwerant]

The fix should now be in 2.11.0!