public String toString() {
        StringJoiner chain = new StringJoiner(", ", getClass().getName() + "{", "}");
        for (TransformationStage<R> transformationStage : transformationStages) {
            chain.add(transformationStage.transformClass().getName());
        }
        return chain.toString();
    }
Represents a chain of {@link Transformation}s to be applied to a {@link ConnectRecord} serially.
@param <T> The type of record included in the {@link ProcessingContext} associated with each record
@param <R> The type of record (must be an implementation of {@link ConnectRecord})
connect/runtime/src/main/java/org/apache/kafka/connect/runtime/TransformationChain.java