CartesianChart的XAxes属性中的Labels属性中含有null值会导致图表无法加载/Null values in XAxes.Labels cause CartesianChart to fail silently without error

[yuan-yp]

定义了变量Axis，将它绑定在WPF的CartesianChart的XAxes属性时，如果变量Axis的Labels属性中含有null值的话，会使整个CartesianChart无法正确加载并且没有报错的提示，如果可以的话，能够有空指针报错会让问题排查更加简单
When binding a variable Axis to the XAxes property of a WPF CartesianChart, if the Labels property of the Axis contains null values, the entire chart fails to load without any error message or exception. This silent failure makes debugging extremely difficult.

**Environment:**​

LiveCharts version: 2.0.0-rc5.4
.NET Framework/.NET Core version: .NET6.0