JVM IR: Don't produce CHECKCASTs on null constants (KT-36650)

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ExpressionCodegen.kt

@@ -718,7 +718,7 @@ class ExpressionCodegen(
             is Float -> mv.fconst(value)
             is Double -> mv.dconst(value)
             is Number -> mv.iconst(value.toInt())
-            else -> mv.aconst(value)
+            else -> if (expression.kind == IrConstKind.Null) return nullConstant else mv.aconst(value)
         }
         return expression.onStack
     }

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/PromisedValue.kt

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.codegen.AsmUtil
 import org.jetbrains.kotlin.codegen.StackValue
 import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.util.parentAsClass
+import org.jetbrains.kotlin.resolve.jvm.AsmTypes
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.org.objectweb.asm.Label
 import org.jetbrains.org.objectweb.asm.Type
@@ -162,3 +163,12 @@ val IrType.unboxed: IrType
 // A Non-materialized value of Unit type that is only materialized through coercion.
 val ExpressionCodegen.unitValue: PromisedValue
     get() = MaterialValue(this, Type.VOID_TYPE, context.irBuiltIns.unitType)
+
+val ExpressionCodegen.nullConstant: PromisedValue
+    get() = object : PromisedValue(this, AsmTypes.OBJECT_TYPE, context.irBuiltIns.nothingNType) {
+        override fun materializeAt(target: Type, irTarget: IrType) {
+            mv.aconst(null)
+        }
+
+        override fun discard() {}
+    }