WASM: Properly handle nullable exported strings

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/BodyGenerator.kt

@@ -369,7 +369,7 @@ class BodyGenerator(val context: WasmFunctionCodegenContext) : IrElementVisitorV
         // Handle complex exported parameters.
         // TODO: This should live as a separate lowering which creates separate shims for each exported function.
         if (context.irFunction.isExported(context.backendContext) &&
-            expression.value.type == irBuiltIns.stringType) {
+            expression.value.type.getClass() == irBuiltIns.stringType.getClass()) {
 
             body.buildCall(context.referenceFunction(wasmSymbols.exportString))
         }

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/WasmModuleCodegenContextImpl.kt

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.defaultType
+import org.jetbrains.kotlin.ir.types.getClass
 import org.jetbrains.kotlin.ir.types.isNothing
 import org.jetbrains.kotlin.ir.util.isFunction
 import org.jetbrains.kotlin.ir.util.parentAsClass
@@ -59,7 +60,7 @@ class WasmModuleCodegenContextImpl(
 
     override fun transformExportedResultType(irType: IrType): WasmType? {
         // Exported strings are passed as pointers to the raw memory
-        if (irType == backendContext.irBuiltIns.stringType)
+        if (irType.getClass() == backendContext.irBuiltIns.stringType.getClass())
             return WasmI32
         return with(typeTransformer) { irType.toWasmResultType() }
     }