private static Boolean createNonExistingCells(TokenBuffer buffer, String fieldName) {
        if (buffer.current() == JsonToken.VALUE_TRUE) {
            return true;
        } else if (buffer.current() == JsonToken.VALUE_FALSE) {
            return false;
        } else {
            throw new IllegalArgumentException("Unknown value '" + buffer.currentText() + "' for '" + MODIFY_CREATE + "' in modify update for field '" + fieldName + "'");
        }
    }
Reader of a "modify" update of a tensor field.
document/src/main/java/com/yahoo/document/json/readers/TensorModifyUpdateReader.java