Cannot have a field with all nil values

[hangxie]

It does not work if a nullable field has null value in all rows, sample code:

package main

import (
	"fmt"

	"github.com/xitongsys/parquet-go-source/local"
	"github.com/xitongsys/parquet-go/writer"
)

type AllTypes struct {
	f1 string  `parquet:"name=f1, type=BYTE_ARRAY, convertedtype=UTF8, encoding=PLAIN_DICTIONARY"`
	f2 *string `parquet:"name=f2, type=BYTE_ARRAY, convertedtype=UTF8, encoding=PLAIN_DICTIONARY"`
}

func main() {
	fw, err := local.NewLocalFileWriter("all-nil.parquet")
	if err != nil {
		fmt.Println("Can't create local file", err)
		return
	}

	pw, err := writer.NewParquetWriter(fw, new(AllTypes), 4)
	if err != nil {
		fmt.Println("Can't create parquet writer", err)
		return
	}

	value := AllTypes{
		f1: "f1",
		f2: nil,
	}
	if err = pw.Write(value); err != nil {
		fmt.Println("Write error", err)
	}
	if err = pw.WriteStop(); err != nil {
		fmt.Println("WriteStop error", err)
		return
	}
	fw.Close()
}

reports:

WriteStop error interface conversion: interface {} is nil, not string

I would suggest to have a consideration of #457 which will make debug a lot easier, error messages like above does not offer any helpful information.

[hangxie]

It turned out to be struct definition need to be uppercased, sorry for false alarm.