POSTGRES ERROR: query string argument of EXECUTE is null

I am am to create this function, but when I call it I get an error of:

query string argument of EXECUTE is null
​

create or replace function test2 ( p_values text[])
language 'plpgsql'
as $body$

declare

l_sql text;
l_sub_id m_subj.m_sub_id%type;

Begin


l_sql:= 'select a.column_value as cpODS,
d.Ps5Dly as item_id,
t1.request_id,
t1.group_name
from (select (coalesce(column_value, ''''::text)) as column_value from unnest($1) as column_value) a
left outer join lab_dim_c d on :9 = d.item_id and d.subject_id = ' || l_sub_id || '
inner join cdf_pass t1 on a.column_value = t1.cpODS';

l_sql := replace(l_sql, ':9','a.column_value');

EXECUTE l_sql USING p_values;/*These variables would replace the $1, $2, $3, $4*/

end;
$body$

CALL test2(array['123435','12434']);


I am clearly passing in values in my function call, and so I do not understand why there is an issue here. Can I have another pair of eyes on this?

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