Prevent raise if business template is not installed

If Business Template is not present, returns None.

product/ERP5/Tool/TemplateTool.py

@@ -172,7 +172,9 @@ class TemplateTool (BaseTool):
         given
       """
       bt = self.getInstalledBusinessTemplate(title)
-      return bt.getRevision()
+      if bt is not None:
+        return bt.getRevision()
+      return None
 
     def getBuiltBusinessTemplatesList(self):
       """Deprecated.

product/ERP5/tests/testTemplateTool.py

@@ -281,6 +281,9 @@ class TestTemplateTool(ERP5TypeTestCase):
     self.assertTrue(300 < self.getPortal()\
         .portal_templates.getInstalledBusinessTemplateRevision('erp5_core'))
 
+    self.assertEquals(None, self.getPortal()\
+        .portal_templates.getInstalledBusinessTemplateRevision('erp5_toto'))
+
   def test_getInstalledBusinessTemplateList(self):
     templates_tool = self.getPortal().portal_templates
     bt5_list = templates_tool.getInstalledBusinessTemplateList()