Imported Upstream version 4.2.0.179

Former-commit-id: 4610231f55806d2a05ed69e5ff3faa7336cc1479

mcs/tests/test-924.cs

@@ -0,0 +1,30 @@
+using System;
+
+class MainClass
+{
+	public static int Main ()
+	{
+		DataFrame df1 = new DataFrame ();
+		DataFrame df2 = new DataFrame ();
+
+		if (df1 != null) 
+		{
+			return 1;
+		}
+
+		return 0;
+	}
+
+	public class DataFrame
+	{
+		public static bool operator ==(DataFrame df1, DataFrame df2)
+		{
+			return df1 is DataFrame;
+		}
+
+		public static bool operator !=(DataFrame df1, DataFrame df2)
+		{
+			return !(df1 == df2);
+		}
+	}
+}