Set context variable to None if no image provided to image templatetag

CHANGELOG.txt

@@ -21,6 +21,7 @@ Changelog
  * Fix: Improve Wagtail logo contrast by adding a background (Brian Edelman, Simon Evans, Ben Enright)
  * Fix: Prevent duplicate notification messages on page locking (Jacob Topp-Mugglestone)
  * Fix: Fix InlinePanel item non field errors not visible (Storm Heg)
+ * Fix: `{% image ... as var %}` now clears the context variable when passed None as an image (Maylon Pedroso)
 
 
 2.8 (03.02.2020)

docs/releases/2.9.rst

@@ -35,6 +35,8 @@ Bug fixes
  * Improved Wagtail logo contrast by adding a background (Brian Edelman, Simon Evans, Ben Enright)
  * Prevent duplicate notification messages on page locking (Jacob Topp-Mugglestone)
  * Rendering of non field errors for InlinePanel items (Storm Heg)
+ * ``{% image ... as var %}`` now clears the context variable when passed None as an image (Maylon Pedroso)
+
 
 Upgrade considerations
 ======================

wagtail/images/templatetags/wagtailimages_tags.py

@@ -97,6 +97,8 @@ class ImageNode(template.Node):
             return ''
 
         if not image:
+            if self.output_var_name:
+                context[self.output_var_name] = None
             return ''
 
         if not hasattr(image, 'get_rendition'):

wagtail/images/tests/test_templatetags.py

@@ -0,0 +1,65 @@
+from django.template import Variable
+from django.test import TestCase
+
+from wagtail.images.models import Image, Rendition
+from wagtail.images.templatetags.wagtailimages_tags import ImageNode
+from wagtail.images.tests.utils import get_test_image_file
+
+
+class ImageNodeTestCase(TestCase):
+
+    @classmethod
+    def setUpTestData(cls):
+        # Create an image for running tests on
+        cls.image = Image.objects.create(
+            title="Test image",
+            file=get_test_image_file(),
+        )
+
+    def test_render_valid_image_to_string(self):
+        """
+        Tests that an ImageNode with a valid image renders an img tag
+        """
+        context = {'image': self.image}
+        node = ImageNode(Variable('image'), 'original')
+
+        rendered = node.render(context)
+
+        self.assertIn('<img alt="Test image"', rendered)
+
+    def test_render_none_to_string(self):
+        """
+        Tests that an ImageNode without image renders an empty string
+        """
+        context = {'image': None}
+        node = ImageNode(Variable('image'), 'original')
+
+        rendered = node.render(context)
+
+        self.assertEqual(rendered, '')
+
+    def test_render_valid_image_as_context_variable(self):
+        """
+        Tests that an ImageNode with a valid image and a context variable name
+        renders an empty string and puts a rendition in the context variable
+        """
+        context = {'image': self.image, 'image_node': 'fake value'}
+        node = ImageNode(Variable('image'), 'original', 'image_node')
+
+        rendered = node.render(context)
+
+        self.assertEqual(rendered, '')
+        self.assertIsInstance(context['image_node'], Rendition)
+
+    def test_render_none_as_context_variable(self):
+        """
+        Tests that an ImageNode without an image and a context variable name
+        renders an empty string and puts None in the context variable
+        """
+        context = {'image': None, 'image_node': 'fake value'}
+        node = ImageNode(Variable('image'), 'original', 'image_node')
+
+        rendered = node.render(context)
+
+        self.assertEqual(rendered, '')
+        self.assertIsNone(context['image_node'])