Bug report

Spreadsheet throws error when opening a xlsx file containing diagonal borders.

Reproduction of the problem

1. Try to open a xlsx file, containing a cell with diagonal borders:
   
   Sample File:
   DiagonalBorderTest.xlsx

Current behavior

Spreadsheet crashes and throws an error Uncaught TypeError: Cannot set property 'color' of undefined

Expected/desired behavior

The file should open.

Environment

• Kendo UI version: 2021.1.330
• Browser: [all]