Order Variable with default value appears twice in Modify Variable Operation

Current Situation:

Users can modify the value of a variable when adding an order using the "Modify Variable" operation. However, if two order variables are defined—one with a value assigned and the other left with its default value (empty)—the variable with the default value appears twice when the "Modify Variable" operation is used while adding order.

Steps to Reproduce:*

• Create a workflow with two order variables.
• Assign a value to one variable and leave the other with its default (empty) value.
• In the Workflows view, click "Add Order."
• Click "Modify Variable."
  → The variable with the empty/default value is displayed twice.

Expected Behavior:

When clicking "Modify Variable," each order variable should be displayed only once, regardless of whether it has a value or not. The operation should not duplicate variables with default (empty) values.