How To Fix /IWBEP/CM_V4_MED389 - Nullable collection not allowed in property '&1'

SAP Error Message - Details

• Message type: E = Error

• Message class: /IWBEP/CM_V4_MED -

• Message number: 389

• Message text: Nullable collection not allowed in property '&1'

Self-Explanatory Message

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Smart SAP Assistant

• What is the cause and solution for SAP error message /IWBEP/CM_V4_MED389 - Nullable collection not allowed in property '&1' ?

  The SAP error message /IWBEP/CM_V4_MED389 Nullable collection not allowed in property '&1' typically occurs in the context of OData services when there is an issue with the definition of a collection property in your OData model. This error indicates that a collection property is defined as nullable, which is not allowed in the context of the OData service.
  Cause:
  
  Nullable Collection Definition: The error arises when a collection property (an array or list of items) is defined in the OData model as nullable. In OData, collections cannot be nullable; they must always be present, even if they are empty.
  Model Configuration: The issue may stem from the way the OData model is configured in the backend, particularly in the metadata definition of the entity type.
  
  Solution:
  To resolve this error, you need to ensure that the collection property is defined correctly in your OData model. Here are the steps to fix the issue:
  
  
  Check the Entity Type Definition:
  
  Go to the definition of the entity type in your OData service.
  Locate the collection property that is causing the error.
  
  
  
  Modify the Property Definition:
  
  Ensure that the collection property is defined as non-nullable. In the metadata, it should look something like this:
  <Property Name="YourCollectionProperty" Type="Collection(YourType)" Nullable="false" />
  
  If it is currently set to Nullable="true", change it to Nullable="false".
  
  
  
  Regenerate the OData Service:
  
  After making changes to the entity type definition, regenerate the OData service to apply the changes.
  You may need to activate the service again in the SAP Gateway.
  
  
  
  Test the Service:
  
  After making the changes and regenerating the service, test the OData service to ensure that the error no longer occurs.
  
  
  
  Related Information:
  
  OData Specification: According to the OData V4 specification, collections must always be present in the response, even if they are empty. This is why nullable collections are not allowed.
  SAP Gateway: If you are using SAP Gateway, ensure that your service is properly configured and that you are following best practices for defining entity types and properties.
  Debugging: If the error persists after making the changes, consider using transaction codes like /IWFND/ERROR_LOG to check for additional error messages or logs that might provide more context.
  
  By following these steps, you should be able to resolve the error and ensure that your OData service functions correctly.