Primitive fields inside unwrapped optional value not considered nullable in schema

[cowtowncoder]

(from https://github.com/FasterXML/jackson-dataformat-avro/issues/29 by @osi)

When generating an avro schema, given:

class A {
 @JsonUnwrapped
 public final Optional<B> b;
}

class B {
  public final boolean flag;
}

The generated schema for A does not consider the 'flag' field to be nullable.