Compiler Error CS0186

Use of null is not valid in this context

The following sample generates CS0186:

// CS0186.cs  
using System;  
using System.Collections;  
  
class MyClass
{  
   static void Main()
   {  
      // Each of the following lines generates CS0186:  
      foreach (int i in null) {}   // CS0186  
      foreach (int i in (IEnumerable) null) { };   // CS0186  
   }  
}