Fix templating when data is empty

Fixes base_template.load and remove_template_definition which fail when
the userdata is empty / None or when the userdata has only one line.

Change-Id: I2ba0e16489049be390b2c9bc1fdf1e1059f54eb1

cloudbaseinit/tests/utils/template_engine/test_base_template.py

@@ -22,6 +22,7 @@ from cloudbaseinit.utils.template_engine import base_template as bt
 class TestBaseTemplateEngine(unittest.TestCase):
 
     @ddt.data((b'', b''),
+              (None, None),
               (b'## template:jinja test', b''),
               (b'## template:jinja \ntest', b'test'))
     @ddt.unpack

cloudbaseinit/tests/utils/template_engine/test_jinja2_template.py

@@ -13,6 +13,7 @@
 #    under the License.
 
 
+import ddt
 import unittest
 try:
     import unittest.mock as mock
@@ -23,6 +24,7 @@ from cloudbaseinit.utils.template_engine.jinja2_template import (
     Jinja2TemplateEngine)
 
 
+@ddt.ddt
 class TestJinja2TemplateEngine(unittest.TestCase):
 
     @mock.patch('cloudbaseinit.utils.template_engine.base_template'
@@ -80,3 +82,13 @@ class TestJinja2TemplateEngine(unittest.TestCase):
             fake_instance_data=fake_instance_data,
             expected_result=expected_result,
             fake_template=fake_template)
+
+    @ddt.data((b'', None),
+              (None, None),
+              (b'## template:jinja \n#ps1 \nmkdir', True),
+              (b'## template:jinja test', None),
+              (b'## template:jinjanone \ntest', None))
+    @ddt.unpack
+    def test_load_template_definition(self, userdata, expected_output):
+        output = Jinja2TemplateEngine().load(userdata)
+        self.assertEqual(expected_output, output)

cloudbaseinit/utils/template_engine/base_template.py

@@ -42,13 +42,23 @@ class BaseTemplateEngine(object):
 
     def load(self, data):
         """Returns True if the template header matches, False otherwise"""
+        if not data:
+            return
+
         template_type_matcher = self._template_matcher.match(data.decode())
+        if not template_type_matcher:
+            return
+
         template_type = template_type_matcher.group(1).lower().strip()
         if self.get_template_type() == template_type:
             return True
 
     @staticmethod
     def remove_template_definition(raw_template):
+        # return the raw template as is if it is None or empty array / dict
+        if not raw_template:
+            return raw_template
+
         # Remove the first line, as it contains the template definition
         template_split = raw_template.split(b"\n", 1)