Handle case where the data for the country is empty.

Signed-off-by: Aivin V. Solatorio <avsolatorio@gmail.com>

services.py

@@ -202,6 +202,14 @@ def get_wdi_data(
                 break
 
             metadata, data_page = json_response
+
+            if data_page is None:
+                if metadata.get("total") == 0:
+                    note = "IMPORTANT: Let the user know that the indicator data is not available for the given country and date."
+                else:
+                    note = "ERROR: The API response is invalid or empty."
+                break
+
             all_data.extend(data_page)
 
             if len(all_data) >= MAX_INFO: