Fix workflows with optional non-default parameter input

where input not provided. Fixes #19328

lib/galaxy/workflow/modules.py

@@ -1610,13 +1610,14 @@ def execute(
         else:
             input_value = step.state.inputs["input"]
         if input_value is None:
-            default_value = step.get_input_default_value(NO_REPLACEMENT)
+            default_value = step.get_input_default_value(None if step.input_optional else NO_REPLACEMENT)
             # TODO: look at parameter type and infer if value should be a dictionary
             # instead. Guessing only field parameter types in CWL branch would have
             # default as dictionary like this.
             if not isinstance(default_value, dict):
                 default_value = {"value": default_value}
-            input_value = default_value.get("value", NO_REPLACEMENT)
+            input_value = default_value.get("value")
+
         input_param = self.get_runtime_inputs(self)["input"]
         # TODO: raise DelayedWorkflowEvaluation if replacement not ready ? Need test
         try:

lib/galaxy_test/workflow/optional_text_param_rescheduling.gxwf-tests.yml

@@ -0,0 +1,12 @@
+- doc: |
+    Test that scheduling succeeds even if step needs rescheduling
+  job:
+    optional_text:
+      type: raw
+      value: null
+  outputs:
+    out:
+      class: File
+      asserts:
+      - that: has_text
+        text: "null"

lib/galaxy_test/workflow/optional_text_param_rescheduling.gxwf.yml

@@ -0,0 +1,30 @@
+class: GalaxyWorkflow
+inputs:
+  optional_text:
+    type: text
+    optional: true
+  when:
+    type: boolean
+    default: true
+outputs:
+  out:
+    outputSource: gx_text_optional/inputs_json
+steps:
+  pick_value:
+    tool_id: pick_value
+    tool_state:
+      style_cond:
+        pick_style: first
+        type_cond:
+          param_type: boolean
+          pick_from:
+          - value: true
+  gx_text_optional:
+    tool_id: gx_text_optional
+    # the when expression requires pick_value to execute, which recapitulates https://github.com/galaxyproject/galaxy/issues/19328
+    when: $(inputs.when)
+    in:
+      parameter:
+        source: optional_text
+      when:
+        source: pick_value/boolean_param