Add 'not selected' option for optional layer parameters in processing model view

rudivs · nyalldawson · commit cb3364f1dcdf · 2018-07-12T09:29:13.000+10:00
Fixes #19329 (https://issues.qgis.org/issues/19329) Optional layer parameters in processing algorithms used in the graphical modeler add an empty string as the default parameter value, which can raise an exception during algorithm execution. This update replaces the default empty string with a default 'Not selected' option. (cherry-picked from 57fb4ef)
diff --git a/python/plugins/processing/gui/wrappers.py b/python/plugins/processing/gui/wrappers.py
@@ -864,10 +864,10 @@ def createWidget(self):
             self.combo = QComboBox()
             layers = self.getAvailableLayers()
             self.combo.setEditable(True)
+            if self.param.flags() & QgsProcessingParameterDefinition.FlagOptional:
+                self.combo.addItem(self.NOT_SELECTED, self.NOT_SET_OPTION)
             for layer in layers:
                 self.combo.addItem(self.dialog.resolveValueDescription(layer), layer)
-            if self.param.flags() & QgsProcessingParameterDefinition.FlagOptional:
-                self.combo.setEditText("")
 
             widget = QWidget()
             layout = QHBoxLayout()
