Gets a value indicating whether the DataGridViewCellStyle.NullValue property has been set.
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Use this property to determine whether the DataGridViewCellStyle.NullValue property has been explicitly set without having to store its default value for comparison. This is useful because the DataGridViewCellStyle.NullValue property has a non-empty default value, unlike most other System.Windows.Forms.DataGridViewCellStyle properties, which have default values such as null, System.Drawing.Color.Empty, or DataGridViewContentAlignment.NotSet.