improve graphql error handling

web/src/app/arrangementer/[slug]/page.tsx

@@ -31,11 +31,16 @@ export async function generateStaticParams() {
   `);
   const { data, error } = await getClient().query(allEventSlugsQuery, {});
 
-  if (data === undefined || error) {
-    throw new Error("failed to generate static params");
+  if (error) {
+    throw new Error(error.message);
+  }
+  if (!data?.pages) {
+    throw new Error(
+      "Failed to generate static params for subpages of /arrangementer"
+    );
   }
 
-  return data?.pages.map((page: any) => ({
+  return data.pages.map((page: any) => ({
     slug: page.slug,
   }));
 }
@@ -47,12 +52,15 @@ export async function generateMetadata(
   const { data, error } = await getClient().query(eventBySlugQuery, {
     slug: params.slug,
   });
-  const event = (data?.event ?? []) as EventFragment[];
 
-  if (!event) {
+  if (error) {
+    throw new Error(error.message);
+  }
+  if (!data?.event) {
     return null;
   }
 
+  const event = data.event as EventFragment;
   const metadata = await getSeoMetadata(event, parent);
   return metadata;
 }
@@ -62,11 +70,14 @@ export default async function Page({ params }: { params: { slug: string } }) {
     slug: params.slug,
   });
 
-  if (data?.event === null || error) {
+  if (error) {
+    throw new Error(error.message);
+  }
+  if (!data?.event) {
     return notFound();
   }
 
-  const event = (data?.event ?? {}) as EventFragment;
+  const event = data.event as EventFragment;
   const eventPig = getEventPig(event);
 
   return (