check for existence of switch instance before introing - fixes #3054

src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts

@@ -447,7 +447,7 @@ export default class InlineComponentWrapper extends Wrapper {
 			`);
 
 			block.builders.intro.add_block(deindent`
-				@transition_in(${name}.$$.fragment, #local);
+				if (${name}) @transition_in(${name}.$$.fragment, #local);
 			`);
 
 			if (updates.length) {

test/runtime/samples/dynamic-component-nulled-out-intro/_config.js

@@ -0,0 +1,5 @@
+export default {
+	test({ component }) {
+		component.visible = true;
+	}
+};

test/runtime/samples/dynamic-component-nulled-out-intro/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	export let visible = false;
+</script>
+
+{#if visible}
+	<svelte:component this={null}/>
+{/if}