ERROR: Access using a 'ZERO' object reference is not possible. (termination: RABAX_STATE)

ERROR: Access using a 'ZERO' object reference is not possible. (termination: RABAX_STATE)

Symptom

When opening an appraisal in the portal, an error is displayed:

Error: 500 SAP Internal Server Error
ERROR: Access using a 'ZERO' object reference is not possible. (termination: RABAX_STATE)

A dump file (this can be found in transaction ST22) is also generated which contains the following:

Category                           ABAP Programming Error
Runtime Errors                   OBJECTS_OBJREF_NOT_ASSIGNED
Except.                              CX_SY_REF_IS_INITIAL