Thanks for contacting Syncfusion support.
We were unable to reproduce the issue. But we suspect that the issue occurs when a column field is not defined in the Grid dataSource and obtained as null value, and hence throws a null exception.
If you still face the issue, share the following information to find the cause of the issue.
1. Client side and server side full code example.
2. Are you performing any Grid operations like filtering\searching before exporting?
3. Essential studio version.
4. An issue reproducing sample if possible or sample hosted link or replicate the issue in the following sample.