Fixed #27024 -- Prevented logging error with empty string as geometry widget value

Thanks Gavin Wahl for the report, and Tim Graham for the review.

tests/gis_tests/geoadmin/tests.py

@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 from django.contrib.gis import admin
 from django.contrib.gis.geos import Point
 from django.test import TestCase, override_settings, skipUnlessDBFeature
+from django.test.utils import patch_logger
 
 from .admin import UnmodifiableAdmin
 from .models import City, site
@@ -71,3 +72,32 @@ class GeoAdminTest(TestCase):
         self.assertFalse(has_changed(initial, data_same))
         self.assertFalse(has_changed(initial, data_almost_same))
         self.assertTrue(has_changed(initial, data_changed))
+
+    def test_olwidget_empty_string(self):
+        geoadmin = site._registry[City]
+        form = geoadmin.get_changelist_form(None)({'point': ''})
+        with patch_logger('django.contrib.gis', 'error') as logger_calls:
+            output = str(form['point'])
+        self.assertInHTML(
+            '<textarea id="id_point" class="vWKTField required" cols="150"'
+            ' rows="10" name="point"></textarea>',
+            output
+        )
+        self.assertEqual(logger_calls, [])
+
+    def test_olwidget_invalid_string(self):
+        geoadmin = site._registry[City]
+        form = geoadmin.get_changelist_form(None)({'point': 'INVALID()'})
+        with patch_logger('django.contrib.gis', 'error') as logger_calls:
+            output = str(form['point'])
+        self.assertInHTML(
+            '<textarea id="id_point" class="vWKTField required" cols="150"'
+            ' rows="10" name="point"></textarea>',
+            output
+        )
+        self.assertEqual(len(logger_calls), 1)
+        self.assertEqual(
+            logger_calls[0],
+            "Error creating geometry from value 'INVALID()' (String or unicode input "
+            "unrecognized as WKT EWKT, and HEXEWKB.)"
+        )