2876102 - ABAPHELP error: Node with key RELATKEY does not exist

In SE38 editor, following error happens when F1 is pressed to start ABAPHELP:

Error in Table Parameter in Tree Model

Class CL_SIMPLE_TREE_MODEL
Method ADD_NODES
Table name: NODE_KEY_TABLE
Errors: Node with key RELATKEY does not exist
Node Key ABAPGET_TIME-STAMP

After the popup is closed, shortdump may happen:

Category ABAP programming error
Runtime Errors OBJECTS_OBJREF_NOT_ASSIGNED
Except. CX_SY_REF_IS_INITIAL
ABAP Program SAPLABAP_DOCU
Application Component BC-ABA-LA

Information on where terminated
The termination occurred in ABAP program or include "SAPLABAP_DOCU", in
"FILL_TREE". The
main program was "RSABAPPROGRAM".

In the source code, the termination point is in line 1952 of include
"LABAP_DOCUP01".
include "LABAP_DOCUP01".
The termination is due to exception "CX_SY_REF_IS_INITIAL" occurring in
procedure "FILL_TREE" "(METHOD)",
but not being handled locally there or being declared in the RAISING
clause.
The procedure is in program "SAPLABAP_DOCU". Its source code begins in line
1891 of
include "LABAP_DOCUP01".

S/4 1909

OBJECTS_OBJREF_NOT_ASSIGNED, ABAP_DOCU_SERVICES, SAPLABAP_DOCU , KBA , BC-ABA-LA , Syntax, Compiler, Runtime , Problem