WPF错误：必须使“Property”具有非 null 值。

解决办法就是用DataTrigger代替Trigger， 然后用Binding+Converter转换为具体非Null值。

比如：

<Style x:Key="DisableStyle" TargetType="Button">
            <Style.Triggers>
                <MultiDataTrigger>
                    <MultiDataTrigger.Conditions>
                        <Condition Binding="{Binding ElementName=ckb1, Path=IsChecked, Converter={StaticResource NullableToBooleanConverter}}" Value="true"></Condition>
                        <Condition Binding="{Binding ElementName=ckb2, Path=IsChecked, Converter={StaticResource NullableToBooleanConverter}}" Value="true"></Condition>
                    </MultiDataTrigger.Conditions>
                    <Setter Property="IsEnabled" Value="False"></Setter>
                </MultiDataTrigger>
            </Style.Triggers>
        </Style>

NullableToBooleanConverter:

public  object  Convert (  object  value  ,  Type  targetType ,  object  parameter ,  CultureInfo  culture  )

        {

             Nullable < bool  >  isCheck  =  value  as  Nullable <  bool >;

             if  ( null  ==  isCheck )

            {

                 return  false  ;

            }

             else

            {

                 return  isCheck  . Value ;

            }

        }