找不到方法：从Framework 4.5降级到4.0时使用UseConsistentNullReferenceBehavior

I have a VS 2012 C#/WPF solution that was originally targeting the .Net Framework 4.5. When I went to deploy it, however, I found that 4.5 does not support WinXP. WinXP is still on the supported list for the 4.0 framework, so I changed all the projects in my solution to target the 4.0 Client framework.I have a VS 2012 C#/WPF solution that was origi