Approach 1:
Set minimum width to the column with null value.
<telerik:DataGridTextColumn
CellContentStyle="{StaticResource textcellStyle}"
HeaderStyle="{StaticResource headerStyle}"
HeaderText="ddd"
PropertyName="KKK"
MinimumWidth="50"
SizeMode="Fixed" />
Approach 2: Set IsResizable to false to the column with null value:
<telerik:DataGridTextColumn
CellContentStyle="{StaticResource textcellStyle}"
HeaderStyle="{StaticResource headerStyle}"
HeaderText="ddd"
PropertyName="KKK"
IsResizable="False"
SizeMode="Fixed" />Regards,
Didi
Progress Telerik