Pay attention to the CRM version when using the SDK NuGet packages

Microsoft publishes the CRM SDK DLLs also as NuGet packages, you can find the list by browsing the crmsdk profile:

https://www.nuget.org/profiles/crmsdk

Because the packages are not separate by CRM version (for example a package for CRM 2015 and a package for CRM 2016) Microsoft simply updates the NuGet package increasing the version.
This can be an issue in some projects as happened to me some days ago. I was working on a plugin for CRM 2015, my project was targeting .NET 4.5.2 and I installed the current version of CoreAssemblies (8.0.1).
The build was successful but the plugin always returned the exception "Value cannot be null".

I spent some time to understand that the problem was the referenced DLL version, so I removed the NuGet package and I installed the 2015 specific version (7.1.1) using the Package Manager Console:

Install-Package Microsoft.CrmSdk.CoreAssemblies -Version 7.1.1

After the plugin worked like a charm.
As reference these are the current versions and the suggested .NET framework to use:

• CRM 2011: 5.0.18 (.NET 4.0)
• CRM 2013: 6.1.1 (.NET 4.0)
• CRM 2015: 7.1.1 (.NET 4.5.2)
• CRM 2016: 8.0.1 (.NET 4.5.2)