uffer containing <TT
CLASS="STRUCTFIELD"
>tg_newtuple</TT
>, or <TT
CLASS="SYMBOL"
>InvalidBuffer</TT
> if there
        is no such tuple or it is not stored in a disk buffer.
       </P
></DD
></DL
></DIV
><P>
   </P
><P
>    A trigger function must return either a
    <TT
CLASS="STRUCTNAME"
>HeapTuple</TT
> pointer or a <TT
CLASS="SYMBOL"
>NULL</TT
> pointer
    (<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> an SQL null value, that is, do not set <TT
CLASS="PARAMETER"
>isNull</TT
> true).
