Minor. Add tests

compiler/testData/codegen/box/inlineClasses/callableReferences/let/nullGeneric.kt

@@ -0,0 +1,10 @@
+// WITH_STDLIB
+// WORKS_WHEN_VALUE_CLASS
+// LANGUAGE: +ValueClasses, +GenericInlineClassParameter
+
+OPTIONAL_JVM_INLINE_ANNOTATION
+value class Value<T: Any>(val value: T)
+
+fun foo(value: Value<String>?) = value?.value
+
+fun box(): String = (null as Value<String>?).let(::foo) ?: "OK"