Problem with PostgreSQL json object (PGobject) to logstash - type cast problem - postgresql

Question

I am trying to index data from a PostgreSQL database to elastic search using logstash. I have a column in the database which is of type JSON. When I run logstash, I get an error called "Missing Converter handling". I do understand that is java/logstash doesn't recognize the JSON type column.
I can typecast the column to "col_name::TEXT" which works fine. However, I need that column as JSON in an elastic search index. Is there any workaround?
Note: Keys in the JSON object is not fixed, it varies.
Logstash postgres query example:
input {
jdbc {
# Postgres jdbc connection string to our database, bot
jdbc_connection_string => "***"
# The user we wish to execute our statement as
jdbc_user => "***"
jdbc_password => "***"
# The path to our downloaded jdbc driver
jdbc_driver_library => "<ja_file_path>"
# The name of the driver class for Postgresql
jdbc_driver_class => "org.postgresql.Driver"
# our query
statement => "SELECT col_1, col_2, col_3, json_col_4 from my_db;"
}
}
filter{
}
output {
stdout { codec => json_lines }
}
Need JSON object from PostgreSQL to elastic search.