diff --git a/php/epntap.php b/php/epntap.php
index 2e632b6..1b6db9c 100644
--- a/php/epntap.php
+++ b/php/epntap.php
@@ -24,6 +24,14 @@ switch ($action) {
 }
 echo json_encode($response);
 
+function getParam($paramName, $default=null) {
+	if(array_key_exists($paramName, $_GET)) {
+		return filter_var($_GET[$paramName], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
+	} else {
+		return $default;
+	}
+}
+
 function resolver() {
 	$input = filter_var($_GET['input'], FILTER_SANITIZE_URL);
 	$resolver_url = "http://voparis-registry.obspm.fr/ssodnet/1/autocomplete?q=%22$input%22";
@@ -111,12 +119,12 @@ function getServices() {
 }
 
 function getNbResults() {
-	$url = filter_var($_GET['url'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$tableName = filter_var($_GET['tableName'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$targetName = filter_var($_GET['targetName'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$productTypes = filter_var($_GET['productTypes'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$timeMin = filter_var($_GET['timeMin'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$timeMax = filter_var($_GET['timeMax'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
+	$url = getParam('url');
+	$tableName = getParam('tableName');
+	$targetName = getParam('targetName');
+	$productTypes = getParam('productTypes');
+	$timeMin = getParam('timeMin');
+	$timeMax = getParam('timeMax');
 
 	$query = "SELECT COUNT(*) AS nb_rows FROM $tableName" . createFilter($targetName, $productTypes, $timeMin, $timeMax);
 	$response = request($url, $query);
@@ -145,16 +153,15 @@ function getNbResults() {
 }
 
 function getGranules() {
-	// TODO: simplify this
-	$url = filter_var($_GET['url'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$tableName = filter_var($_GET['tableName'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$targetName = filter_var($_GET['targetName'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$productTypes = filter_var($_GET['productTypes'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$timeMin = filter_var($_GET['timeMin'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$timeMax = filter_var($_GET['timeMax'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$start = filter_var($_GET['start'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$limit = filter_var($_GET['limit'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
-	$nbRes = filter_var($_GET['nbRes'], FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_LOW);
+	$url = getParam('url');
+	$tableName = getParam('tableName');
+	$targetName = getParam('targetName');
+	$productTypes = getParam('productTypes');
+	$timeMin = getParam('timeMin');
+	$timeMax = getParam('timeMax');
+	$start = getParam('start');
+	$limit = getParam('limit');
+	$nbRes = getParam('nbRes');
 
 	$filter = createFilter($targetName, $productTypes, $timeMin, $timeMax);
 	$query = "SELECT TOP $limit * FROM $tableName $filter OFFSET $start";
--
libgit2 0.21.2