diff --git a/searx/utils.py b/searx/utils.py
index 6c7b6b68a..43a7578d7 100644
--- a/searx/utils.py
+++ b/searx/utils.py
@@ -6,6 +6,8 @@
 """
 import re
 import importlib
+import importlib.util
+import types
 
 from typing import Optional, Union, Any, Set, List, Dict, MutableMapping, Tuple, Callable
 from numbers import Number
@@ -45,8 +47,8 @@ _STORAGE_UNIT_VALUE: Dict[str, int] = {
     'KiB': 1000,
 }
 
-_XPATH_CACHE = {}
-_LANG_TO_LC_CACHE = {}
+_XPATH_CACHE: Dict[str, XPath] = {}
+_LANG_TO_LC_CACHE: Dict[str, Dict[str, str]] = {}
 
 
 class _NotSetClass:  # pylint: disable=too-few-public-methods
@@ -150,7 +152,7 @@ def html_to_text(html_str: str) -> str:
     return s.get_text()
 
 
-def extract_text(xpath_results, allow_none: bool = False):
+def extract_text(xpath_results, allow_none: bool = False) -> Optional[str]:
     """Extract text from a lxml result
 
     * if xpath_results is list, extract the text from each result and concat the list
@@ -264,7 +266,9 @@ def extract_url(xpath_results, base_url) -> str:
         raise ValueError('Empty url resultset')
 
     url = extract_text(xpath_results)
-    return normalize_url(url, base_url)
+    if url:
+        return normalize_url(url, base_url)
+    raise ValueError('URL not found')
 
 
 def dict_subset(dictionnary: MutableMapping, properties: Set[str]) -> Dict:
@@ -366,7 +370,7 @@ def _get_lang_to_lc_dict(lang_list: List[str]) -> Dict[str, str]:
 
 # babel's get_global contains all sorts of miscellaneous locale and territory related data
 # see get_global in: https://github.com/python-babel/babel/blob/master/babel/core.py
-def _get_from_babel(lang_code, key: str):
+def _get_from_babel(lang_code: str, key: str):
     match = get_global(key).get(lang_code.replace('-', '_'))
     # for some keys, such as territory_aliases, match may be a list
     if isinstance(match, str):
@@ -374,7 +378,7 @@ def _get_from_babel(lang_code, key: str):
     return match
 
 
-def _match_language(lang_code, lang_list=[], custom_aliases={}) -> Optional[str]:  # pylint: disable=W0102
+def _match_language(lang_code: str, lang_list=[], custom_aliases={}) -> Optional[str]:  # pylint: disable=W0102
     """auxiliary function to match lang_code in lang_list"""
     # replace language code with a custom alias if necessary
     if lang_code in custom_aliases:
@@ -396,10 +400,12 @@ def _match_language(lang_code, lang_list=[], custom_aliases={}) -> Optional[str]
             return new_code
 
     # try to get the any supported country for this language
-    return _get_lang_to_lc_dict(lang_list).get(lang_code, None)
+    return _get_lang_to_lc_dict(lang_list).get(lang_code)
 
 
-def match_language(locale_code, lang_list=[], custom_aliases={}, fallback='en-US') -> str:  # pylint: disable=W0102
+def match_language(  # pylint: disable=W0102
+    locale_code, lang_list=[], custom_aliases={}, fallback: Optional[str] = 'en-US'
+) -> Optional[str]:
     """get the language code from lang_list that best matches locale_code"""
     # try to get language from given locale_code
     language = _match_language(locale_code, lang_list, custom_aliases)
@@ -437,12 +443,16 @@ def match_language(locale_code, lang_list=[], custom_aliases={}, fallback='en-US
     return language or fallback
 
 
-def load_module(filename: str, module_dir: str):
+def load_module(filename: str, module_dir: str) -> types.ModuleType:
     modname = splitext(filename)[0]
-    filepath = join(module_dir, filename)
+    modpath = join(module_dir, filename)
     # and https://docs.python.org/3/library/importlib.html#importing-a-source-file-directly
-    spec = importlib.util.spec_from_file_location(modname, filepath)
+    spec = importlib.util.spec_from_file_location(modname, modpath)
+    if not spec:
+        raise ValueError(f"Error loading '{modpath}' module")
     module = importlib.util.module_from_spec(spec)
+    if not spec.loader:
+        raise ValueError(f"Error loading '{modpath}' module")
     spec.loader.exec_module(module)
     return module
 
@@ -477,7 +487,7 @@ def ecma_unescape(string: str) -> str:
     return string
 
 
-def get_string_replaces_function(replaces: Dict[str, str]) -> Callable:
+def get_string_replaces_function(replaces: Dict[str, str]) -> Callable[[str], str]:
     rep = {re.escape(k): v for k, v in replaces.items()}
     pattern = re.compile("|".join(rep.keys()))