[BUG] NullPointerException when uploading file to Submodel Element (File) with null value

[JS-Aibel]

Describe the bug
I encountered a NullPointerException when attempting to upload a file to a Submodel Element (File) that does not have a value. The error occurs specifically when the value is not set. However, if the value is set to an empty string (""), the upload proceeds without any errors.

To Reproduce
Steps to reproduce the behavior:

1. Create an AAS with a submodel that includes an empty Submodel Element (File).
2. Upload the AAS to the AAS environment.
3. Use the endpoint: PUT /submodels/{submodelIdentifier}/submodel-elements/{idShortPath}/attachment to upload a file.

Error

• Response Status: 500
• AAS Env Log Message: NullPointerException: Cannot invoke "String.isBlank()" because "fileName" is null

Expected behavior
The file should upload successfully without errors, regardless of whether the Submodel Element (File)'s value is null or an empty string.

BaSyx (please complete the following information):

• BaSyx Version [v2.0]
• AAS Version [DotAAS V3]

BaSyx configuration
Default with MongoDB