title: Empty key fields for MaterialBOMItem of API_BILL_OF_MATERIAL_SRV Version 2 using SAP Cloud SDK JavaScript
body: <p>I am trying to update/delete a bill of material item using the SAP Cloud SDK JavaScript (version 1.12.0).
  The item belongs to a group BOM, i.e. the property "plant" is an empty string.</p>
  
  <p>This results in the following self-explaining error message (example for PATCH request):</p>
  
  <pre><code>Error: OData update request failed!
      ...
  Caused by:
  Error: patch request to https://&lt;host&gt;:&lt;port&gt;/sap/opu/odata/sap/API_BILL_OF_MATERIAL_SRV;v=0002 $failed!
      ...
  Caused by:
  Error: The value:  of the key: Plant is not nullable, please set the value.
      ...
  </code></pre>
  
  <p>This behaviour is consistent with the documentation of the entity <code>MaterialBOMItem</code> of the service <code>API_BILL_OF_MATERIAL_SRV (Version 2)</code> (<a href="https://api.sap.com/api/API_BILL_OF_MATERIAL_SRV_0002/resource" rel="nofollow noreferrer">https://api.sap.com/api/API_BILL_OF_MATERIAL_SRV_0002/resource</a>)
  where updating and removing entities of MaterialBOMItem require "Plant" and some other fields.</p>
  
  <p>In detail, this affects the routes PATCH and DELETE which require these properties: BillOfMaterial, BillOfMaterialCategory, BillOfMaterialVariant, BillOfMaterialVersion, BillOfMaterialItemNodeNumber, HeaderChangeDocument, Material, Plant.</p>
  
  <p>For some of them an empty value may be valid (e.g. empty plant for group BOM).</p>
  
  <p>However, although "Plant" is marked as required it can be left empty
  when using the PATCH/UPDATE endpoints of API_BILL_OF_MATERIAL_SRV. This way I can update/delete a group BOM item. </p>
  
  <p>Should the SDK support this behaviour as well?</p>