How To Fix WL490 - Operation '&' between data type '&' and '&' not allowed

SAP Error Message - Details

• Message type: E = Error

• Message class: WL - Workflow: run-time messages

• Message number: 490

• Message text: Operation '&' between data type '&' and '&' not allowed

What causes this issue?

You have tried to compare two container elements or expressions or link
them in an arithmetic operation (addition etc.). However, the selected
operation is not allowed or not worthwhile on the underlying data
types.
Example:
numbers cannot be compared with objects
character strings cannot be added to numbers
the result of an operation must be compatible with the operands used
assignment to a constant is not possible
The following abbreviations are used in the message:
l,,Integers (ABAP Dictionary data type <AB>Int1</>, <AB>Int2</>,
<AB>Int4</>)
P,,Packed numbers with decimal places and signs (<AB>Dec</>, <AB>Packed
</>)
N,,Character string with numeric values (<AB>Numc</>)
C,,Character string (<AB>Character</>)
D,,Date (<AB>Date</>)
T,,Time (<AB>Time</>)
O o,,Objects from the Business Object Repository

How to fix this error?

Only use elements or expressions which can be linked with the selected
operation, that is only define the operation between compatible ABAP
data types or between object types.
You can only calculate using numbers (type I, P).
Exception: the following operations are permitted with date/time:
'Date - Date' returns an integer
'Date - number' returns a date
'Time - number' returns a time
'Time - Time' returns an integer
You can only compare numbers with numbers (type I, P, N), date with
date, time with time, character-based types (C, N). Objects can be
compared to see whether they are the same (o).
The type of the result of an arithmetic operation or an assignment must
be compatible with the type of the operand(s).
Hexadecimal numbers (X, RAW) and floating point numbers (F, FLTP) are
not supported in container operations at present. If necessary, define
object methods to implement operations with these types in a program.
Further information can be found in the online help in the ABAP editor
on the ABAP key words <AB>Data</> and <AB>Move</>.

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