Json Groovy examples not working

[madmas]

Hi,
I attempt to make use of the JSON datatype using groovy.

I was looking at the examples in https://www.julienviet.com/reactive-pg-client/guide/groovy/index.html

Unfortunately the statement

def tuple = Tuple.of(Json.create(Json.create(null)), Json.create(Json.create([
  foo:"bar"
])), Json.create(Json.create(null)))

fails with

Unexpected error occurred: Invalid json value null with class io.reactiverse.reactivex.pgclient.data.Json
 java.lang.IllegalArgumentException: Invalid json value null with class io.reactiverse.reactivex.pgclient.data.Json
 	at io.reactiverse.pgclient.data.Json.create(Json.java:33)
 	at io.reactiverse.reactivex.pgclient.data.Json.create(Json.java:63)
 	at io.reactiverse.reactivex.pgclient.data.Json$create.call(Unknown Source)
 	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
 	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:115)
 	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:127)

As I was wondering about the duplicate Json.create, but when I remove that I get

 Unexpected error occurred: Invalid json value {foo=bar} with class java.util.LinkedHashMap
 java.lang.IllegalArgumentException: Invalid json value {foo=bar} with class java.util.LinkedHashMap
	at io.reactiverse.pgclient.data.Json.create(Json.java:33)
	at io.reactiverse.reactivex.pgclient.data.Json.create(Json.java:63)
	at io.reactiverse.reactivex.pgclient.data.Json$create.call(Unknown Source)

How would someone use it properly?