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

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

django/contrib/gis/admin/widgets.py

@@ -31,7 +31,7 @@ class OpenLayersWidget(Textarea):
 
         # If a string reaches here (via a validation error on another
         # field) then just reconstruct the Geometry.
-        if isinstance(value, six.string_types):
+        if value and isinstance(value, six.string_types):
             try:
                 value = GEOSGeometry(value)
             except (GEOSException, ValueError) as err:

django/contrib/gis/forms/widgets.py

@@ -46,7 +46,7 @@ class BaseGeometryWidget(Widget):
     def render(self, name, value, attrs=None):
         # If a string reaches here (via a validation error on another
         # field) then just reconstruct the Geometry.
-        if isinstance(value, six.string_types):
+        if value and isinstance(value, six.string_types):
             value = self.deserialize(value)
 
         if value:

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.)"
+        )

tests/gis_tests/test_geoforms.py

@@ -2,6 +2,7 @@ from django.contrib.gis import forms
 from django.contrib.gis.geos import GEOSGeometry
 from django.forms import ValidationError
 from django.test import SimpleTestCase, override_settings, skipUnlessDBFeature
+from django.test.utils import patch_logger
 from django.utils.html import escape
 
 
@@ -84,6 +85,48 @@ class GeometryFieldTest(SimpleTestCase):
         form = PointForm(data={'pt': 'POINT(5 23)'}, initial={'pt': point})
         self.assertFalse(form.has_changed())
 
+    def test_field_string_value(self):
+        """
+        Initialization of a geometry field with a valid/empty/invalid string.
+        Only the invalid string should trigger an error log entry.
+        """
+        class PointForm(forms.Form):
+            pt1 = forms.PointField(srid=4326)
+            pt2 = forms.PointField(srid=4326)
+            pt3 = forms.PointField(srid=4326)
+
+        form = PointForm({
+            'pt1': 'SRID=4326;POINT(7.3 44)',  # valid
+            'pt2': '',  # empty
+            'pt3': 'PNT(0)',  # invalid
+        })
+
+        with patch_logger('django.contrib.gis', 'error') as logger_calls:
+            output = str(form)
+
+        self.assertInHTML(
+            '<textarea id="id_pt1" class="vSerializedField required" cols="150"'
+            ' rows="10" name="pt1">POINT (7.3 44)</textarea>',
+            output
+        )
+        self.assertInHTML(
+            '<textarea id="id_pt2" class="vSerializedField required" cols="150"'
+            ' rows="10" name="pt2"></textarea>',
+            output
+        )
+        self.assertInHTML(
+            '<textarea id="id_pt3" class="vSerializedField required" cols="150"'
+            ' rows="10" name="pt3"></textarea>',
+            output
+        )
+        # Only the invalid PNT(0) should trigger an error log entry
+        self.assertEqual(len(logger_calls), 1)
+        self.assertEqual(
+            logger_calls[0],
+            "Error creating geometry from value 'PNT(0)' (String or unicode input "
+            "unrecognized as WKT EWKT, and HEXEWKB.)"
+        )
+
 
 @skipUnlessDBFeature("gis_enabled")
 class SpecializedFieldTest(SimpleTestCase):