AI-generated Key Takeaways
- 
          The operation can be either creating or updating a user list. 
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          The update_maskfield uses a FieldMask to determine which resource fields are modified during an update.
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          The operationfield can be one of three types:create,update, orremove.
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          A createoperation does not require a resource name for the new user list, while anupdateoperation requires a valid resource name.
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          A removeoperation requires a resource name in the formatcustomers/{customer_id}/userLists/{user_list_id}.
A single operation (create, update) on a user list.
| Fields | |
|---|---|
| 
 | FieldMask that determines which resource fields are modified in an update. | 
| Union field 
 | |
| 
 | Create operation: No resource name is expected for the new user list. | 
| 
 | Update operation: The user list is expected to have a valid resource name. | 
| 
 | 
 Remove operation: A resource name for the removed user list is expected, in this format: 
 |