more error reporting

diff --git a/librarian/formats/cover/evens/__init__.py b/librarian/formats/cover/evens/__init__.py
index a4b721c..e07f78b 100644 (file)
--- a/librarian/formats/cover/evens/__init__.py
+++ b/librarian/formats/cover/evens/__init__.py
@@ -19,9 +19,12 @@ class EvensCover(Cover):
     logo_bottom = 100
 
     def set_images(self, ctx):
-        cover_url = self.doc.meta.get(DCNS('relation.coverimage.url'))[0]
+        try:
+            cover_url = self.doc.meta.get(DCNS('relation.coverimage.url'))[0]
+        except IndexError:
+            raise BuildError('No cover specified (metadata field relation.coverimage.url missing)')
         if not cover_url:
-            raise BuildError('No cover specified')
+            raise BuildError('No cover specified (metadata field relation.coverimage.url empty)')
         if cover_url.startswith('file://'):
             cover_url = ctx.files_path + urllib.quote(cover_url[7:])
         try: