(avro) Compatibility issue because Schema validation error

In avro 1.9.2 -

```
public Object get(String key) {
Field field = this.schema.getField(key);
return field == null ? null : this.values[field.pos()];
}
```

getString method was handling null value and returning null to caller, but in 1.10.X version this function throwing exception org.apache.avro.AvroRuntimeException: Not a valid schema field:. This causing issue as code was not sensitive to schema earlier we treat common reader for all different schema but its failing if we upgrade to latest version of Jar.
Please take a note.