only adding popular choices if it is not None

webpage.py

@@ -373,11 +373,12 @@ class page():
         self.add_content("<button type='submit' onclick='combine()'>Submit</button>\n", indent=2)
         self.add_content("</div>\n")
         self.add_content("<div class='row justify-content-center'>\n")
-        for i in popular_options:
-            self.add_content("<button type='button' class='btn btn-light' "
-                             "onclick='combine(\"{}\")' "
-                             "style='margin-left:0.25em; margin-right:0.25em; "
-                             "margin-top: 1.0em'>{}</button>\n".format(i, i), indent=2)
+        if popular_options:
+            for i in popular_options:
+                self.add_content("<button type='button' class='btn btn-light' "
+                                 "onclick='combine(\"{}\")' "
+                                 "style='margin-left:0.25em; margin-right:0.25em; "
+                                 "margin-top: 1.0em'>{}</button>\n".format(i, i), indent=2)
         self.add_content("</div>")
         self.add_content("<div class='row justify-content-center' id='corner_plot'>\n")
         self.add_content("<canvas id='canvas' width='600' height='600'></canvas>\n", indent=2)