fix: address feedback

lib/EasyPost/Requestor.php

@@ -55,9 +55,7 @@ public static function utf8($value)
      */
     private static function _encodeObjects($data)
     {
-        if ($data === "") {
-            return null;
-        } elseif (is_null($data)) {
+        if (is_null($data)) {
             return array();
         } elseif ($data instanceof EasypostResource) {
             return array("id" => self::utf8($data->id));
@@ -68,9 +66,7 @@ private static function _encodeObjects($data)
         } elseif (is_array($data)) {
             $resource = array();
             foreach ($data as $k => $v) {
-                if (empty($data)) {
-                    return null;
-                } elseif (!is_null($v)) {
+                if (!is_null($v) and ($v !== "") and (!is_array($v) or !empty($v))) {
                     $resource[$k] = self::_encodeObjects($v);
                 }
             }

test/EasyPost/Test/ShipmentTest.php

@@ -218,13 +218,15 @@ public function testCreateEmptyObjects()
             ),
             "options" => null,
             "tax_identifiers" => null,
+            "reference" => "",
         ));
 
         $this->assertInstanceOf('\EasyPost\Shipment', $shipment);
         $this->assertIsString($shipment->id);
         $this->assertStringMatchesFormat('shp_%s', $shipment->id);
         $this->assertNotEmpty($shipment->options); // The EasyPost API populates some default values here
-        $this->assertEmpty($shipment->customs_info->customs_items);
+        $this->assertEmpty($shipment->customs_info);
+        $this->assertNull($shipment->reference);
     }
 
     /**