Gracefully handle identifiers not being set

invenio_theme_tuw/views.py

@@ -20,9 +20,10 @@ blueprint = Blueprint(
 @blueprint.app_template_filter("tuw_doi_identifier")
 def tuw_doi_identifier(identifiers):
     """Extract DOI from sequence of identifiers."""
-    for identifier in identifiers:
-        if identifier.get("scheme") == "doi":
-            return identifier.get("identifier")
+    if identifiers is not None:
+        for identifier in identifiers:
+            if identifier.get("scheme") == "doi":
+                return identifier.get("identifier")
 
 
 @blueprint.app_template_global("tuw_cite_as")
@@ -47,9 +48,11 @@ def tuw_cite_as(record_metadata):
         version if version.lower().startswith("v") else "Version {}".format(version)
     )
     fmt_resource_type = vocabulary.get_title_by_dict(resource_type)
-    fmt_doi = (
-        doi if doi.lower().startswith("http") else "https://doi.org/{}".format(doi)
-    )
+    fmt_doi = ""
+    if doi is not None:
+        fmt_doi = (
+            doi if doi.lower().startswith("http") else "https://doi.org/{}".format(doi)
+        )
 
     # format the author names roughly according to the APA logic:
     # https://research.moreheadstate.edu/c.php?g=107001&p=695202
@@ -69,5 +72,5 @@ def tuw_cite_as(record_metadata):
         fmt_resource_type,
         publisher,
         fmt_doi,
-    )
+    ).strip()
     return text