Handle not being able to get elements via JS

qutebrowser/browser/hints.py

@@ -566,6 +566,10 @@ class HintManager(QObject):
 
     def _start_cb(self, elems):
         """Initialize the elements and labels based on the context set."""
+        if elems is None:
+            message.error("There was an error while getting hint elements")
+            return
+
         filterfunc = webelem.FILTERS.get(self._context.group, lambda e: True)
         elems = [e for e in elems if filterfunc(e)]
         if not elems:

qutebrowser/browser/navigate.py

@@ -112,6 +112,10 @@ def prevnext(*, browsertab, win_id, baseurl, prev=False,
         window: True to open in a new window, False for the current one.
     """
     def _prevnext_cb(elems):
+        if elems is None:
+            message.error("There was an error while getting hint elements")
+            return
+
         elem = _find_prevnext(prev, elems)
         word = 'prev' if prev else 'forward'
 

qutebrowser/browser/webengine/webenginetab.py

@@ -392,8 +392,13 @@ class WebEngineElements(browsertab.AbstractElements):
 
         Args:
             callback: The callback to call with the found elements.
+                      Called with None if there was an error.
             js_elems: The elements serialized from javascript.
         """
+        if js_elems is None:
+            callback(None)
+            return
+
         elems = []
         for js_elem in js_elems:
             elem = webengineelem.WebEngineElement(js_elem, tab=self._tab)