Optional string in avro scheme

[Dzmitry Hancharou]

Hello all,

I want to convert json with optional string field into binary avro file.

The following scheme is used:
Optional.avsc:
    {
        "namespace": "Namespace",
        "type": "record",
        "name": "Optional",
        "fields": [
            {
                "name": "opt",
                "type": ["null", "string"],
                "default": null
            },
            {
                "name": "req",
                "type": "string"
            }
        ]
    }

optional.json: {"req": "xxx"}

When I run "java -jar avro-tools-1.7.7.jar fromjson --schema-file
Optional.avsc optional.json > optional.avro", get exception:
Exception in thread "main" org.apache.avro.AvroTypeException: Expected
field name not found: opt
at org.apache.avro.io.JsonDecoder.doAction(JsonDecoder.java:477)
at org.apache.avro.io.parsing.Parser.advance(Parser.java:88)
at org.apache.avro.io.JsonDecoder.advance(JsonDecoder.java:139)
at org.apache.avro.io.JsonDecoder.readIndex(JsonDecoder.java:429)
at org.apache.avro.io.ResolvingDecoder.doAction(ResolvingDecoder.java:290)
at org.apache.avro.io.parsing.Parser.advance(Parser.java:88)
at org.apache.avro.io.ResolvingDecoder.readIndex(ResolvingDecoder.java:267)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:155)
at
org.apache.avro.generic.GenericDatumReader.readField(GenericDatumReader.java:193)
at
org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:183)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:151)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:142)
at org.apache.avro.tool.DataFileWriteTool.run(DataFileWriteTool.java:99)
at org.apache.avro.tool.Main.run(Main.java:84)
at org.apache.avro.tool.Main.main(Main.java:73)

When I change optional.json to {"opt": "yyy", "req": "xxx"}, I get
Exception in thread "main" org.apache.avro.AvroTypeException: Expected
start-union. Got VALUE_STRING
at org.apache.avro.io.JsonDecoder.error(JsonDecoder.java:697)
at org.apache.avro.io.JsonDecoder.readIndex(JsonDecoder.java:441)
at org.apache.avro.io.ResolvingDecoder.doAction(ResolvingDecoder.java:290)
at org.apache.avro.io.parsing.Parser.advance(Parser.java:88)
at org.apache.avro.io.ResolvingDecoder.readIndex(ResolvingDecoder.java:267)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:155)
at
org.apache.avro.generic.GenericDatumReader.readField(GenericDatumReader.java:193)
at
org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:183)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:151)
at
org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:142)
at org.apache.avro.tool.DataFileWriteTool.run(DataFileWriteTool.java:99)
at org.apache.avro.tool.Main.run(Main.java:84)
at org.apache.avro.tool.Main.main(Main.java:73)

What I'm doing wrong?

Thanks,
Dmitry