Return the Id of the parameter associated with this constraint. 
   Namespace:   Autodesk.Revit.DB.Structure  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2012 
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Return Value
The Id of the parameter, or InvalidElementId if the constraint does not have one.Remarks
 Most subclasses of RebarShapeConstraint require a parameter.