fix in convex hull

extensions/fablabchemnitz/convexhull.py

@@ -76,9 +76,10 @@ class ConvexHull(inkex.EffectExtension):
         etree.SubElement(g, inkex.addNS('path', 'svg' ), line_attribs) 
 
     def effect(self):
+    
+        if len(self.svg.selected) > 0:
             global output_nodes, points
-        #Loop through all the selected items in Inkscape
-        for node in self.svg.selected.values():
+            
             #create numpy array of nodes
             n_array = []
                     
@@ -113,7 +114,11 @@ class ConvexHull(inkex.EffectExtension):
             path = 'polygon'
             makeGroup = False
             paths_clone_transform = None
-        self.joinWithNode(path, pdata, makeGroup, paths_clone_transform )
+            self.joinWithNode(path, pdata, makeGroup, paths_clone_transform)
+            
+        else:
+            inkex.errormsg('Please select some paths first.')
+            return
             
 if __name__ == '__main__':
     ConvexHull().run()