diff --git a/TODO b/TODO
index 0c19b03..82cceac 100644
--- a/TODO
+++ b/TODO
@@ -13,10 +13,6 @@
 
 * libowlps
 
-- Remove timestamp_to_ms()
-   This function is used only by the aggregator to test if a TIMESTAMP
-   is null. We should create a function to test that, instead of
-   converting to ms every time.
 - mac_bytes_to_string(): do not malloc anymore.
 
 
diff --git a/owlps-aggregator/owlps-aggregatord.c b/owlps-aggregator/owlps-aggregatord.c
index 325180f..92e74cc 100644
--- a/owlps-aggregator/owlps-aggregatord.c
+++ b/owlps-aggregator/owlps-aggregatord.c
@@ -688,7 +688,7 @@ void got_request(owl_captured_request request)
       memcpy(tmp_request->mobile_mac_addr_bytes,
              request.mobile_mac_addr_bytes, 6) ;
       // Explicit packet:
-      if (owl_timestamp_to_ms(request.request_time) != 0)
+      if (! owl_timestamp_is_null(request.request_time))
         // Transmission time on the mobile:
         tmp_request->request_time = request.request_time ;
       // Implicit packet:
@@ -710,7 +710,7 @@ void got_request(owl_captured_request request)
   else // If the request list exists already
     { // we search the list for the request
       // Explicit packet:
-      if (owl_timestamp_to_ms(request.request_time) != 0)
+      if (! owl_timestamp_is_null(request.request_time))
         {
           while (tmp_request != NULL)
             { // Research criterion: MAC and transmission time
@@ -745,7 +745,7 @@ void got_request(owl_captured_request request)
           memcpy(tmp_request->mobile_mac_addr_bytes,
                  request.mobile_mac_addr_bytes, 6) ;
           // Explicit packet:
-          if (owl_timestamp_to_ms(request.request_time) != 0)
+          if (! owl_timestamp_is_null(request.request_time))
             // Transmission time on the mobile:
             tmp_request->request_time = request.request_time ;
           // Implicit packet: