private static Schema readSchema(Schema tableSchema, Schema projectedSchema) {
        Preconditions.checkNotNull(tableSchema, "Table schema can't be null");
        return projectedSchema == null ? tableSchema : projectedSchema;
    }
Copy from iceberg-flink:iceberg-flink-1.15:1.3.1
inlong-sort/sort-flink/sort-flink-v1.15/sort-connectors/iceberg/src/main/java/org/apache/inlong/sort/iceberg/source/reader/RowDataReaderFunction.java