presto-parquet/src/main/java/io/prestosql/parquet/reader/BinaryColumnReader.java/BinaryColumnReader/readValue
class BinaryColumnReader:    @Override
    protected void readValue(BlockBuilder blockBuilder, Type type)
    {
        if (definitionLevel == columnDescriptor.getMaxDefinitionLevel()) {
            Binary binary = valuesReader.readBytes();
            Slice value;
            if (binary.length() == 0) {
                value = EMPTY_SLICE;
            }
            else {
                value = wrappedBuffer(binary.getBytes());
            }
            if (isVarcharType(type)) {
                value = truncateToLength(value, type);
            }
            if (isCharType(type)) {
                value = truncateToLengthAndTrimSpaces(value, type);
            }
            type.writeSlice(blockBuilder, value);
        }
        else if (isValueNull()) {
            blockBuilder.appendNull();
        }
    }