How To Fix WL387 - Result of operation '& & &' cannot be of type '&'

SAP Error Message - Details

• Message type: E = Error

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

• Message number: 387

• Message text: Result of operation '& & &' cannot be of type '&'

What causes this issue?

The following abbreviations are used in the message:
'I': whole numbers (ABAP data type Int1, Int2, Int4)
'P': packed numbers with decimal places and +/- signs (Dec, Packed)
'N': character string with numerical values (Numc)
'C': character strings (Character)
'D': date
'T': time
'O' or 'o': objects from the Business Object Repository

How to fix this error?

Only use elements or expressions that can be linked with the required
operation, that is, define the operation only between compatiable ABAP
data types or between object types:
You can only calculate with numbers (types I, P). As well as the basic
arithmetical operations (+ - * /), DIV operations (whole number
division) and MOD operations (modulo) are supported.
With date/time, only the following operations are allowed:
'Date - Date' result: whole number
'Date - Number' result: date
'Time - Number' result: time
'Time - Time' result: whole number.
You can only compare numbers with numbers (type I, P, N), dates with
dates, times with times, character-based types (C, N) or objects the
same as each other (o).
The result of a calculation or an assignment must be compatible in type
with the operand(s) and must not lead to an overflow, that is, the
result element selected must be large enough.
Hexadecimal numbers (X, RAW) and floating point numbers (F, FLTP) are
not supported in container operations at present. If applicable, define
object methods to implement operations with these types in a program.
You can find more information in the ABAP editor online help under the
keywords 'Data' and 'Move'.

Error message extract from SAP system. Copyright SAP SE.