add a null check before using attrib (#978)

* resolves issue #973

add a null check before using attrib

* Add pytest_httpserver and unit test

* Remove live server URL

* Mark online

---------

Co-authored-by: sethg <sethg@geographika.co.uk>

Author: pvgenuchten

owslib/iso.py

@@ -224,11 +224,14 @@ def __init__(self, md=None):
             self.charset = None
         else:
             self.id = md.attrib.get('id')
-            self.languagecode = md.find(
-                util.nspath_eval('gmd:languageCode/gmd:LanguageCode', namespaces)).attrib.get('codeListValue')
-            self.charset = md.find(
-                util.nspath_eval('gmd:characterEncoding/gmd:MD_CharacterSetCode', namespaces)).attrib.get(
-                'codeListValue')
+            self.languagecode = None
+            languagecode = md.find(util.nspath_eval('gmd:languageCode/gmd:LanguageCode', namespaces))
+            if languagecode is not None:
+                self.languagecode = languagecode.attrib.get('codeListValue')
+            self.charset = None
+            charset = md.find(util.nspath_eval('gmd:characterEncoding/gmd:MD_CharacterSetCode', namespaces))
+            if charset is not None:
+                self.charset = charset.attrib.get('codeListValue')
 
 
 class CI_Date(object):

requirements-dev.txt

@@ -2,6 +2,7 @@
 flake8
 pytest
 pytest-cov
+pytest_httpserver 
 pytest-socket
 Pillow
 tox