do not crash when config.yml is 0 bytes or empty of data

fdroidserver/common.py

@@ -362,6 +362,8 @@ def read_config(opts=None):
         logging.debug(_("Reading '{config_file}'").format(config_file=config_file))
         with open(config_file, encoding='utf-8') as fp:
             config = yaml.safe_load(fp)
+        if not config:
+            config = {}
     elif os.path.exists(old_config_file):
         logging.warning(_("""{oldfile} is deprecated, use {newfile}""")
                         .format(oldfile=old_config_file, newfile=config_file))

tests/common.TestCase

@@ -1675,6 +1675,17 @@ class CommonTest(unittest.TestCase):
         self.assertIsNone(config.get('stats_server'))
         self.assertIsNotNone(config.get('char_limits'))
 
+    def test_with_zero_size_config(self):
+        """It should set defaults if config file has nothing in it"""
+        testdir = tempfile.mkdtemp(prefix=inspect.currentframe().f_code.co_name, dir=self.tmpdir)
+        os.chdir(testdir)
+        open('config.yml', 'w').close()
+        self.assertTrue(os.path.exists('config.yml'))
+        self.assertFalse(os.path.exists('config.py'))
+        config = fdroidserver.common.read_config(fdroidserver.common.options)
+        self.assertIsNone(config.get('stats_server'))
+        self.assertIsNotNone(config.get('char_limits'))
+
     def test_with_config_yml(self):
         """Make sure it is possible to use config.yml alone."""
         testdir = tempfile.mkdtemp(