[PostgreSQL timestamp parameter: could not determine data type of parameter $1]

OK, I realised it was a PostgreSQL error. The solution is to force PostgreSQL to interpret the parameter as a timestamp

SELECT *FROM logWHERE CASE  WHEN $P{timestampFrom}::timestamp IS NULL THEN TIMESTAMP >= '-infinity'  ELSE TIMESTAMP >= $P{timestampFrom}  END[/code]

[PostgreSQL timestamp parameter: could not determine data type of parameter $1]

I'm really struggling to get my query to work against my PostgreSQL database. Essentially, my query can be delimited by a timestamp, a parameter that the user can input, but which can also be empty. If no timestamp is provided, I must tell PostgreSQL to use '-infinity' instead. I tried writing the conditional statement below, but I get the error 'Could not determine data type of parameter $1' Can anyone tell me what's wrong with my query?

SELECT *FROM logWHERE CASE  WHEN $P{timestampFrom} IS NULL THEN timestamp >= '-infinity'  ELSE timestamp >= $P{timestampFrom}  END[/code]

$P{timestampFrom} is a sql.Timestamp parameter.