diff --git a/pyoaev/configuration/sources.py b/pyoaev/configuration/sources.py
index 43a5b88..aeb5385 100644
--- a/pyoaev/configuration/sources.py
+++ b/pyoaev/configuration/sources.py
@@ -14,7 +14,7 @@ def get(cls, env_var: str) -> str | None:
         :return: value of the env var, or None if not found
         :rtype: str | None
         """
-        return os.getenv(env_var)
+        return os.getenv(env_var) if env_var else None
 
 
 class DictionarySource:
@@ -23,7 +23,7 @@ class DictionarySource:
     # this is quite hacky
     # it only strictly handles two levels of keys in a dict
     @classmethod
-    def get(cls, config_key_path: list[str], source_dict: dict) -> str | None:
+    def get(cls, config_key_path: list[str] | None, source_dict: dict) -> str | None:
         """Gets the value for the specified env var
 
         :param config_key_path: the two-level dictionary path to the config key
@@ -34,6 +34,9 @@ def get(cls, config_key_path: list[str], source_dict: dict) -> str | None:
         :return: value for the config key at specified path, or None if not found
         :rtype: str | None
         """
+        if config_key_path is None:
+            return None
+
         assert (
             isinstance(config_key_path, list)
             and len(config_key_path) == 2