techdocs: make emptyState input optional on entityContent extension

Signed-off-by: MT Lewis <mtlewis@users.noreply.github.com>

.changeset/fifty-trainers-watch.md

@@ -0,0 +1,6 @@
+---
+'@backstage/plugin-techdocs': patch
+---
+
+Make `emptyState` input optional on `entity-content:techdocs` extension so that
+the default empty state extension works correctly.

plugins/techdocs/api-report-alpha.md

@@ -229,7 +229,9 @@ const _default: FrontendPlugin<
           ConfigurableExtensionDataRef<
             React_2.JSX.Element,
             'core.reactElement',
-            {}
+            {
+              optional: true;
+            }
           >,
           {
             singleton: true;

plugins/techdocs/src/alpha.tsx

@@ -157,10 +157,13 @@ const techDocsReaderPage = PageBlueprint.make({
  */
 const techDocsEntityContent = EntityContentBlueprint.makeWithOverrides({
   inputs: {
-    emptyState: createExtensionInput([coreExtensionData.reactElement], {
-      singleton: true,
-      optional: true,
-    }),
+    emptyState: createExtensionInput(
+      [coreExtensionData.reactElement.optional()],
+      {
+        singleton: true,
+        optional: true,
+      },
+    ),
   },
   factory(originalFactory, context) {
     return originalFactory(