code: @Override
    public FieldVisitor visitField(int access,
                                   String name,
                                   String description,
                                   String signature,
                                   Object value) {
      fields.add(new FieldInfo(access,
          name,
          description,
          signature,
          value));
      return null;
    }
docs: "Visit" a field.
  
  @param access      field access modifiers, etc.
  @param name        field name
  @param description field description
  @param signature   field signature
  @param value       field value, if any
  @return null.