Handle missing optional Tags in OpenSearch descriptions

owslib/opensearch.py

@@ -167,7 +167,7 @@ def __init__(self, md):
         self.outputencoding = testXMLValue(val)
 
         val = md.find(nspath_eval('os:Tags', namespaces))
-        self.tags = testXMLValue(val).split()
+        self.tags = (testXMLValue(val) or '').split()
 
         val = md.find(nspath_eval('os:Contact', namespaces))
         self.contact = testXMLValue(val)

tests/test_opensearch.py

@@ -0,0 +1,27 @@
+import pytest
+
+from owslib.opensearch import OpenSearch
+
+
+@pytest.mark.parametrize('tags_xml, expected_tags', [
+    ('', []),
+    ('<Tags/>', []),
+    ('<Tags>   </Tags>', []),
+    ('<Tags>earth observation</Tags>', ['earth', 'observation']),
+])
+def test_opensearch_description_optional_tags(tags_xml, expected_tags):
+    xml = f'''<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
+        <ShortName>Example search</ShortName>
+        <Description>Search public observations</Description>
+        <Url type="application/atom+xml"
+             template="https://example.com/search?q={{searchTerms}}"/>
+        {tags_xml}
+    </OpenSearchDescription>'''
+
+    client = OpenSearch('https://example.com/opensearch', xml=xml)
+
+    assert client.description.tags == expected_tags
+    assert client.description.shortname == 'Example search'
+    assert client.description.urls['application/atom+xml']['template'] == (
+        'https://example.com/search?q={searchTerms}'
+    )