Senseless null in when (KT-2457 frontend part)

compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/SenselessNullInWhen.kt

@@ -0,0 +1,10 @@
+//KT-2457 Verify error when comparing not null value with null in when
+
+package kt2457
+
+fun foo(i: Int) : Int =
+    when (i) {
+        1 -> 1
+        <!SENSELESS_NULL_IN_WHEN!>null<!> -> 1
+        else -> 1
+    }