diff --git a/image_prediction/transformer/transformers/response.py b/image_prediction/transformer/transformers/response.py
index 4703411..42d0f22 100644
--- a/image_prediction/transformer/transformers/response.py
+++ b/image_prediction/transformer/transformers/response.py
@@ -132,13 +132,13 @@ def build_image_info(data: dict) -> dict:
 def parse_env_var(prefix, table=None):
     table = table or os.environ
     head = first(filter(lambda s: s == prefix, table))
-    if not head:
-        logger.warning(f"Found no environment variable with prefix '{prefix}'.")
-    else:
+    if head:
         try:
             return parse_env_var_value(table[head])
         except ParsingError as err:
             logger.warning(err)
+    else:
+        return None
 
 
 def parse_env_var_value(env_var_value):