a stored procedure ..with integer as the parameter

i have a stored procedure

insert_table(integer)
which does "insert into table (x) value ($1)";

now in my client i call the stored procedure as

select insert_table("3");

it works fine and inserts 3 into the table

but suppose i give

select insert_table("");

it gives an error ...saying " invalid input syntax for integer: "

please suggest a solution to this problem

thanks,
reagrds
surabhi