Fix edge case for model arguments Parameter conversion

Signed-off-by: Elliot Gunton <elliotgunton@gmail.com>

src/hera/workflows/_mixins.py

@@ -587,6 +587,13 @@ def _build_arguments(self) -> Optional[ModelArguments]:
         if normalized_arguments is None:
             return None
         elif isinstance(normalized_arguments, ModelArguments):
+            # Special case as Parameter is a subclass of ModelParameter
+            # We need to convert Parameters to ModelParameters
+            if normalized_arguments.parameters:
+                normalized_arguments.parameters = [
+                    ModelParameter.parse_obj(p.dict()) if isinstance(p, Parameter) else p
+                    for p in normalized_arguments.parameters
+                ]
             return normalized_arguments
 
         from hera.workflows.workflow_template import WorkflowTemplate

tests/test_unit/test_mixins.py

@@ -1,6 +1,6 @@
 import pytest
 
-from hera.workflows import Env, Parameter
+from hera.workflows import Env, Parameter, Workflow
 from hera.workflows._mixins import ArgumentsMixin, ContainerMixin, EnvMixin, IOMixin
 from hera.workflows.models import (
     Arguments as ModelArguments,
@@ -113,6 +113,30 @@ def test_model_arguments_value_is_not_normalized_to_list(self):
         assert args_mixin.arguments == ModelArguments()
 
 
+    def test_build_arguments_of_parameter_converted(self):
+        args_mixin = ArgumentsMixin(
+            arguments=[
+                Parameter(name="my-param-1"),
+                Parameter(name="my-param-2"),
+            ]
+        )
+        built_args = args_mixin._build_arguments()
+        assert built_args and built_args.parameters == [
+            ModelParameter(name="my-param-1"),
+            ModelParameter(name="my-param-2"),
+        ]
+
+    def test_build_workflow(self):
+        with Workflow(
+            name="test",
+            arguments=ModelArguments(parameters=[Parameter(name="test", value="value")]),
+        ) as w:
+            pass
+
+        workflow = w.build()
+        assert workflow.spec.arguments.parameters == [ModelParameter(name="test", value="value")]
+
+
 class TestEnvMixin:
     def test_list_normalized_to_list(self):
         env_mixin = EnvMixin(