Checks to see if the specified custom data exists. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 18.0.0.0 (18.2.0.0) 
  Since:  2018 
Syntax
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Parameters
- customDataId
-  Type:  System Int32  
 The custom data identifier.