workflows: don't try substituting images with non-images (#17174)

tests/test_workflows.py

@@ -1931,6 +1931,21 @@ def test_export_to_model_image(pub):
     # check the image has been replaced by the one from the formdata
     assert zinfo.file_size == len(image_data)
 
+    # check with missing data or wrong kind of data
+    for field_value in (None, 'wrong kind'):
+        formdata = formdef.data_class()()
+        formdata.data = {'3': field_value}
+        formdata.just_created()
+        formdata.store()
+        pub.substitutions.feed(formdata)
+
+        item.perform(formdata)
+
+        zfile = zipfile.ZipFile(formdata.evolution[-1].parts[0].filename, mode='r')
+        zinfo = zfile.getinfo('Pictures/10000000000000320000003276E9D46581B55C88.jpg')
+        # check the original image has been left
+        assert zinfo.file_size == 580
+
 def test_global_timeouts(pub):
     FormDef.wipe()
     Workflow.wipe()

wcs/wf/export_to_model.py

@@ -436,6 +436,8 @@ class ExportToModel(WorkflowStatusItem):
                         variable_image = self.compute(name)
                     except:
                         continue
+                    if not hasattr(variable_image, 'get_content'):
+                        continue
                     image = [x for x in node.getchildren() if x.tag == DRAW_IMAGE][0]
                     new_images[image.attrib.get(XLINK_HREF)] = variable_image