=== modified file 'share/extensions/inkex.py'
--- share/extensions/inkex.py	2014-11-25 19:49:28 +0000
+++ share/extensions/inkex.py	2015-07-10 06:42:54 +0000
@@ -207,7 +207,7 @@
             x = self.unittouu( xattr[0] + 'px' )
             y = self.unittouu( yattr[0] + 'px')
             doc_height = self.unittouu(self.document.getroot().get('height'))
-            if x and y:
+            if x and y and doc_height is not None:
                 self.view_center = (float(x), doc_height - float(y)) # FIXME: y-coordinate flip, eliminate it when it's gone in Inkscape
 
     def getselected(self):
@@ -340,19 +340,22 @@
         unit = re.compile('(%s)$' % '|'.join(self.__uuconv.keys()))
         param = re.compile(r'(([-+]?[0-9]+(\.[0-9]*)?|[-+]?\.[0-9]+)([eE][-+]?[0-9]+)?)')
 
-        p = param.match(string)
-        u = unit.search(string)    
-        if p:
-            retval = float(p.string[p.start():p.end()])
+        if string is not None:
+            p = param.match(string)
+            u = unit.search(string)    
+            if p:
+                retval = float(p.string[p.start():p.end()])
+            else:
+                retval = 0.0
+            if u:
+                try:
+                    return retval * (self.__uuconv[u.string[u.start():u.end()]] / self.__uuconv[self.getDocumentUnit()])
+                except KeyError:
+                    pass
+            else: # default assume 'px' unit
+                return retval / self.__uuconv[self.getDocumentUnit()]
         else:
-            retval = 0.0
-        if u:
-            try:
-                return retval * (self.__uuconv[u.string[u.start():u.end()]] / self.__uuconv[self.getDocumentUnit()])
-            except KeyError:
-                pass
-        else: # default assume 'px' unit
-            return retval / self.__uuconv[self.getDocumentUnit()]
+            retval = None
 
         return retval