When I run this query on "enterprisedb 9.2", it raises an error: 

    select quote_nullable(to_date('09-02-2014 ','dd-MM-yyyy'))::date;

Error:

>     LINE 1: select quote_nullable(to_date('09-02-2014 ','dd-MM-yyyy'))::...
>                    ^
>     HINT:  Could not choose a best candidate function. You might need to add explicit type casts.
>     ********** Error **********
>     
>     ERROR: function quote_nullable(timestamp without time zone) is not unique
>     SQL state: 42725
>     Hint: Could not choose a best candidate function. You might need to add explicit type casts.
>     Character: 8

Please tell me what is happening here. Why is the function `quote_nullable(timestamp without time zone)` not unique?