Looks like the variable has to be initialized with something different than null to work, e.g.

LOCAL zz as Integer
zz=0
zz = null
=MESSAGEBOX(STR(zz,5))

without zz=0 it gives the error.

Interestingly, that

local zz as Character
zz=null
=messagebox(val(zz)) && Should give an error too according to Help on VAL

works.

By default, all variables are created with logical type, e.g.

=MESSAGEBOX(TYPE('zz')) returns L, that's why STR doesn't work.

>

>zz = .NULL.
>? ISNULL(zz) ---> .T.
>
>? STR(zz,5) ---> Error:  Function argument value, type, or count is invalid
>? STR(.NULL.,5) ---> .NULL.
>
>? zz+"AA" ---> Operator/Operand type mismatch
>? .NULL. + "AA" ---> .NULL.
>
>? NVL(zz+"AA","xxxxxx") ---> Operator/Operand type mismatch
>? NVL(zz,"xxxxxx") ---> "xxxxxx"
>
>USE myTable
>REPLACE c1 WITH .NULL.
>
>? c1 + "AA" ---> .NULL.
>SCATTER MEMVAR
>? m.c1 + "AA" ---> .NULL.
>
>zz=c1
>? zz + "AA" ---> .NULL.
>
>zz = .NULL.
>? zz + "AA" ---> .NULL.
>
>RELEASE zz
>zz = .NULL.
>and all the errors return
>
>
>

>
>Why do variables directly assigned .NULL. not seem to work correctly while fields and SCATTERed variables give the expected results?
>
>Thanks........Rich