[Bug]: Issue with AvroGenericRecordToStorageApiProto.java handling nullable arrays

What happened?

I've encountered an issue with the AvroGenericRecordToStorageApiProto.java class in Apache Beam, which is responsible for converting an Avro generic record into a proto object for writing to BigQuery using the Storage API.

The class contains two primary methods for handling the conversion:

private TableFieldSchema fieldDescriptorFromAvroField(Schema.Field field)
private static Object toProtoValue(FieldDescriptor fieldDescriptor, Schema avroSchema, Object value)

These methods handle array types effectively when the array in the Avro schema is defined as follows:

{
  "name": "simple_array",
  "type": "array",
  "items": "string",
  "default": []
}

However, the application crashes when a nullable array is used, such as:

{
  "name": "simple_array",
  "type": [
    "null",
    {
      "type": "array",
      "items": "string"
    }
  ],
  "default": null
}

This issue seems to stem from the handling of nullable arrays in the conversion methods.

Issue Priority

Priority: 3 (minor)

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apache / beam