Provide clearer error message when repository entry is empty

test/bad.repos

@@ -0,0 +1,4 @@
+repositories:
+  empty_entry:
+  missing_url:
+    type: git

test/test_commands.py

@@ -16,6 +16,7 @@
 REPOS2_FILE = os.path.join(os.path.dirname(__file__), 'list2.repos')
 TEST_WORKSPACE = os.path.join(
     os.path.dirname(os.path.dirname(__file__)), 'test_workspace')
+BAD_REPOS_FILE = os.path.join(os.path.dirname(__file__), 'bad.repos')
 
 CI = os.environ.get('CI') == 'true'  # Travis CI / Github actions set: CI=true
 svn = which('svn')
@@ -326,6 +327,11 @@ def test_validate(self):
         expected = get_expected_output('validate_hide')
         self.assertEqual(output, expected)
 
+        output = run_command(
+            'validate', ['--input', BAD_REPOS_FILE])
+        expected = get_expected_output('validate_bad')
+        self.assertEqual(output, expected)
+
     @unittest.skipIf(not svn and not CI, '`svn` was not found')
     @unittest.skipIf(not hg and not CI, '`hg` was not found')
     def test_validate_svn_and_hg(self):

test/validate_bad.txt

@@ -0,0 +1,2 @@
+Repository 'empty_entry' is empty
+Repository 'missing_url' does not provide the necessary information: 'url'

vcstool/commands/import_.py

@@ -102,6 +102,12 @@ def get_repos_in_vcstool_format(repositories):
     for path in repositories:
         repo = {}
         attributes = repositories[path]
+        if not attributes:
+            print(
+                ansi('yellowf') + (
+                    "Repository '%s' is empty" % path) + ansi('reset'),
+                file=sys.stderr)
+            continue
         try:
             repo['type'] = attributes['type']
             repo['url'] = attributes['url']