Altering functions cast

We use NULLIF() for adding [1|0|null] according to the
evalution of nullif('x','') into boolean columns.
Where x is [1|0|null], which if it's an empty string
(x='') then we add NULL cause NULLIF says if '' == ''
then return NULL into boolean.

An example wrapper function for this with an integer
cast:

CREATE FUNCTION nullif_always_int(text) RETURNS
integer AS '
SELECT nullif($1,'''')::int;
' LANGUAGE SQL;

I was hoping I could do something simliar with
booleans if possible?

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