substr() does't return null string

[Denis Shirokov]

hello,

( gawk 4.2.1 )


according to The GNU Awk User’s Guide ( at
https://www.gnu.org/software/gawk/manual/gawk.html#Bug-address ):

...If start is greater than the number of characters in the string,
substr() returns the null string...

the following example shows that substr() return empty string ( "" )
instead of null value:

BEGIN{

        t = ""
        
        a = substr( t, 1 )
        
        print "DATA: " a "'"

        if ( a == 0 && a == "" )
                
                print "== NULL"
        
        else
                
                print "!= NULL"

        }

as we see that substr() start character parameter ( 1 ) is higher than
the length of t ( 0 ).
but followed checking returned by substr() result shows that it is not
equal to null:

DATA: '
!= NULL

in my opinion current behaviour of substr() is more useful than
behaviour implemented in documentation because in my code i have some
places with like:

return substr(...) ""

exactly to prevent returning null value and always force it as the empty string

thnx
Denis