private void unwrapSchemaMapping(Processing processing) {
        List<DocumentOperation> documentOperations = processing.getDocumentOperations();
        for (int i = 0; i < documentOperations.size(); i++) {
            if (documentOperations.get(i) instanceof DocumentPut putOperation) {
                if (putOperation.getDocument() instanceof DocumentOperationWrapper proxy) {
                    documentOperations.set(i, new DocumentPut(putOperation, ((DocumentPut) proxy.getWrappedDocumentOperation()).getDocument()));
                }
            }
        }
    }
The DocumentUpdate object a processor should work on. The one in args, or schema mapped.

@return a DocumentUpdate
docproc/src/main/java/com/yahoo/docproc/Call.java