@Override
    public void putExtraOption(java.lang.String key, Object value)
    {
        if (extraOptions.put(key, value) != null)
        {
            final Proto proto;
            final java.lang.String ofOwner;
            if (owner != null)
            {
                // message field
                proto = owner.getProto();
                ofOwner = " of " + owner.getRelativeName();
            }
            else if (ev != null)
            {
                // enum field/value
                proto = enumGroup.getProto();
                ofOwner = " of the enum " + enumGroup.getRelativeName();
            }
            else
            {
                proto = null;
                ofOwner = "";
            }

            throw err("The field " + name + ofOwner +
                    " contains a duplicate option: " + key, proto);
        }
    }
Represents an enum field defined in a {@link Message}.

@author David Yu
@created Dec 19, 2009
protostuff-parser/src/main/java/io/protostuff/parser/EnumField.java