Fixed a path->geos bug for empty paths.

lib/cartopy/mpl/patch.py

@@ -201,7 +201,9 @@ def path_to_geos(path, force_ccw=False):
         # If geom is a Polygon and is contained within the last geom in
         # collection, add it to its list of internal polygons, otherwise
         # simple append it as a  new external geom.
-        if (len(collection) > 0 and
+        if geom.is_empty:
+            pass
+        elif (len(collection) > 0 and
                 isinstance(collection[-1][0], Polygon) and
                 isinstance(geom, Polygon) and
                 collection[-1][0].contains(geom.exterior)):

lib/cartopy/tests/mpl/test_patch.py

@@ -0,0 +1,40 @@
+# (C) British Crown Copyright 2015, Met Office
+#
+# This file is part of cartopy.
+#
+# cartopy is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the
+# Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# cartopy is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with cartopy.  If not, see <http://www.gnu.org/licenses/>.
+
+from __future__ import (absolute_import, division, print_function)
+
+import six
+import unittest
+
+from matplotlib.path import Path
+
+import cartopy.mpl.patch as cpatch
+
+
+class Test_path_to_geos(unittest.TestCase):
+    def test_empty_polyong(self):
+        p = Path([[0, 0], [0, 0], [0, 0], [0, 0],
+                  [0, 0], [0, 0], [0, 0], [0, 0]],
+                 codes=[1, 2, 2, 79,
+                        1, 2, 2, 79])
+        geom = cpatch.path_to_geos(p)
+        self.assertEqual(len(geom), 0)
+
+
+if __name__ == '__main__':
+    import nose
+    nose.runmodule(argv=['-s', '--with-doctest'], exit=False)