Deserialization error when using union for string type

Hi

I am using fastDesrializer for a file written using avro 1.8.2 , whenever parsing using fastdesrializer code , i run into
`Illegal union index for ... ` error ?
Any idea what could be the possible reason ?

Start by reproducing the failure in fastDeserializer with the file written by Avro 1.8.2 and capture the complete union index error. Compare the writer and reader schemas, especially the union containing the string type, to identify the incompatible assumption. Done means the cause is isolated and a focused fix or clear compatibility guidance is available.

Written by the indexing model from the issue text.