Reading schema information

Sorry for missing the email subject in my previous email !

I am trying to get some information about a coloum using the method:

DatabaseMetaData.getString("IS_GENERATEDCOLUMN")

However it is throwing an exception:

org.postgresql.util.PSQLException: The column name IS_GENERATEDCOLUMN
was not found in this ResultSet.

Based on javadoc for getColumns method:

http://docs.oracle.com/javase/7/docs/api/java/sql/DatabaseMetaData.html#getColumns(java.lang.String,%20java.lang.String,%20java.lang.String,%20java.lang.String)

We have:

IS_GENERATEDCOLUMN String => Indicates whether this is a generated column

YES --- if this a generated column
NO --- if this not a generated column
empty string --- if it cannot be determined whether this is a generated column

My questions is, is this a bug ? if not, how can I obtain this
information about a column (if it's generated or not) ?

Thank you.