ignore none as epub metadata value

oml/media/__init__.py

@@ -41,7 +41,6 @@ def metadata(f, from_=None):
     metadata_opf = os.path.join(os.path.dirname(from_ or f), 'metadata.opf')
     if os.path.exists(metadata_opf):
         opf_info = opf.info(metadata_opf)
-
     for key in (
         'title', 'author', 'date', 'publisher', 'description',
         'language', 'textsize', 'pages',

oml/media/epub.py

@@ -75,7 +75,7 @@ def info(epub):
         info = ET.fromstring(z.read(opf[0]))
         metadata = info.findall('{http://www.idpf.org/2007/opf}metadata')[0]
         for e in metadata.getchildren():
-            if e.text:
+            if e.text and e.text not in ('unknown', 'none'):
                 key = e.tag.split('}')[-1]
                 key = {
                     'creator': 'author',