java.lang.UnsupportedOperationException: STRING is not a supported type.

[datngxtiens]

I'm using with changeCase type: com.github.jcustenborder.kafka.connect.transform.common.ChangeCase$Key from Kafka Confluent to convert data key from upper case to lowercase.

After a while of running, the connector threw exception java.lang.UnsupportedOperationException: STRING is not a supported type.
Executing stage 'TRANSFORMATION' with class 'org.apache.kafka.connect.runtime.TransformationStage', where source record is = SourceRecord

java.lang.UnsupportedOperationException: STRING is not a supported type. at com.github.jcustenborder.kafka.connect.transform.common.BaseTransformation.processString(BaseTransformation.java:47) at com.github.jcustenborder.kafka.connect.transform.common.BaseTransformation.process(BaseTransformation.java:141) at com.github.jcustenborder.kafka.connect.transform.common.ChangeCase$Key.apply(ChangeCase.java:108) at org.apache.kafka.connect.runtime.TransformationStage.apply(TransformationStage.java:57) at org.apache.kafka.connect.runtime.TransformationChain.lambda$transformRecord$0(TransformationChain.java:73) at org.apache.kafka.connect.runtime.errors.RetryWithToleranceOperator.execAndRetry(RetryWithToleranceOperator.java:190) at org.apache.kafka.connect.runtime.errors.RetryWithToleranceOperator.execAndHandleError(RetryWithToleranceOperator.java:224) at org.apache.kafka.connect.runtime.errors.RetryWithToleranceOperator.execute(RetryWithToleranceOperator.java:166) at org.apache.kafka.connect.runtime.TransformationChain.transformRecord(TransformationChain.java:73) at org.apache.kafka.connect.runtime.TransformationChain.apply(TransformationChain.java:53) at org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.sendRecords(AbstractWorkerSourceTask.java:401) at org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.execute(Abstra ctWorkerSourceTask.java:367) at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:229) at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:284) at org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.run(AbstractWorkerSourceTask.java:78) at org.apache.kafka.connect.runtime.isolation.Plugins.lambda$withClassLoader$1(Plugins.java:181) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:829)

Search through the log and see only one field thrown at the exception is: keySchema=Schema{STRING}. It's of much help if you can tell hat kind of behaviour is this and how to fix this issue. Thanks is advance