erp5_trade: getInventoryList will use portal_categories 's uid if section_category is empty

portal.portal_simulation.getInventoryList(section_category='', src__=True)
use query like
AND (`related_stock_section_category_uid_1_category`.`category_uid` = 281(Uid of portal_categories)

bt5/erp5_trade/SkinTemplateItem/portal_skins/erp5_trade/Base_getBySiteCurrentStockList.py

 result_list = []
+if section_category:
+  kw['section_category'] = section_category
 for brain in context.portal_simulation.getCurrentInventoryList(
     node_category=node_category,
-    section_category=section_category,
     group_by_resource=True,
     group_by_variation=True,
     group_by_node=False,

product/ERP5/tests/testTradeReports.py

@@ -931,6 +931,20 @@ class TestTradeReports(ERP5ReportTestCase):
 
     self.tic()
 
+  def testStockReport_when_section_category_is_empty(self):
+    self._createInventoryForStockReportTest()
+    request = self.portal.REQUEST
+    request.form['at_date'] = DateTime(2006, 4, 4)
+    request.form['node_category'] = 'site/demo_site_A'
+    request.form['section_category'] = ''
+
+    line_list = self.portal.inventory_module.Base_viewStockReportBySite.listbox.\
+        get_value('default',
+                  render_format='list', REQUEST=self.portal.REQUEST)
+
+    data_line_list = [l for l in line_list if l.isDataLine()]
+    self.assertEqual(1, len(data_line_list))
+
   def testStockReport_old_date(self):
     """
     Old date