2415310 - Error: "Message type " " is unknown" when implementing a note using Note Assistant

When implementing a note using Note Assistant, a runtime error occurs with the following ST22 dump:

Category               ABAP Programming Error
Runtime Errors         MESSAGE_TYPE_UNKNOWN
ABAP Program           SAPLSCWU
Application Component  BC-UPG-NA
Date and Time          DD.MM.YYYY HH:MM:SS 

 Short text
     Message type " " is unknown. 

 What happened?
     Error in the ABAP Application Program
     The current ABAP program "SAPLSCWU" had to be terminated because it has
     come across a statement that unfortunately cannot be executed. 

 What can you do?
     Note down which actions and inputs caused the error.
 
     To process the problem further, contact you SAP system
     administrator.

     Using Transaction ST22 for ABAP Dump Analysis, you can look
     at and manage termination messages, and you can also
     keep them for a long time. 

 Error analysis
     Only message types A, E, I, W, S, and X are allowed.

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• SAP Netweaver 7.x

SAP NetWeaver 7.0 ; SAP NetWeaver 7.3 ; SAP NetWeaver 7.4 ; SAP NetWeaver 7.5 ; SAP enhancement package 1 for SAP NetWeaver 7.0 ; SAP enhancement package 1 for SAP NetWeaver 7.3 ; SAP enhancement package 2 for SAP NetWeaver 7.0 ; SAP enhancement package 3 for SAP NetWeaver 7.0

KBA , BC-UPG-NA , Note Assistant , Problem