KT-2838 Type inference failed on passing null as a nullable argument

#KT-2838 fixed

compiler/testData/diagnostics/tests/inference/regressions/kt2838.kt

@@ -0,0 +1,17 @@
+//KT-2838 Type inference failed on passing null as a nullable argument
+package a
+
+fun foo<T>(a: T, b: Map<T, String>?) = b?.get(a)
+fun bar<T>(a: T, b: Map<T, String>) = b.get(a)
+
+fun test(a: Int) {
+    foo(a, null)
+    <!TYPE_INFERENCE_TYPE_CONSTRUCTOR_MISMATCH!>bar<!>(a, null)
+}
+fun test1(a: Int) {
+    <!UNREACHABLE_CODE!>foo(a, throw Exception())<!>
+}
+
+fun test2(a: Int) {
+    <!UNREACHABLE_CODE!>bar(a, throw Exception())<!>
+}