Warning: React.createElement: type is invalid -- expected a string (for built-in components) or a class/function (for composite components) but got: undefined.

[cha0s]

import SortableTree from 'react-sortable-tree';
import theme from 'react-sortable-tree-theme-file-explorer';

const Project = ({project: {label, tree}}) => (
  <div className="project">
    <h2 className="project__title">{label}</h2>
    <SortableTree
      theme={theme}
      treeData={tree}
    />
  </div>
);

Gives:

Warning: React.createElement: type is invalid -- expected a string (for built-in components)
or a class/function (for composite components) but got: undefined. You likely forgot to export
your component from the file it's defined in, or you might have mixed up default and named imports.

Check the render method of `SortableTree`.

When I look in node_modules/react-sortable-tree/dist/index.esm.js, the default export is:

var SortableTree = function SortableTree(props) {
  return React.createElement(DndProvider, {
    backend: HTML5Backend
  }, React.createElement(SortableTreeWithoutDndContext, props));
};

So, I:

> console.log(DndProvider);
undefined

A little more inspection:

$ node
Welcome to Node.js v14.15.1.
Type ".help" for more information.
> require('react-dnd')
{
  DragDropContext: [Getter],
  DragDropContextProvider: [Getter],
  DragLayer: [Getter],
  DragSource: [Getter],
  DropTarget: [Getter]
}
> require('react-dnd/package.json').version
'2.5.4'

...that's a very old version. More inspection:

> require('react-sortable-tree-theme-file-explorer/package.json').dependencies['react-dnd'];
'2.5.4'
> require('react-sortable-tree-theme-file-explorer/package.json').version;
'2.0.0'

It appears this project is badly out of date and completely broken.