Introduction with empty message raises exception
when making an introduction and leaving the introduction message blank I get this exception:
```
java.lang.IllegalArgumentException: null
at org.briarproject.briar.introduction.MessageEncoderImpl.encodeRequestMessage(MessageEncoderImpl.java:114)
at org.briarproject.briar.introduction.AbstractProtocolEngine.sendRequestMessage(AbstractProtocolEngine.java:115)
at org.briarproject.briar.introduction.IntroducerProtocolEngine.onLocalRequest(IntroducerProtocolEngine.java:230)
at org.briarproject.briar.introduction.IntroducerProtocolEngine.onRequestAction(IntroducerProtocolEngine.java:76)
at org.briarproject.briar.introduction.IntroductionManagerImpl.makeIntroduction(IntroductionManagerImpl.java:363)
at org.briarproject.briar.desktop.introduction.IntroductionViewModel$makeIntroduction$1.invoke(IntroductionViewModel.kt:77)
at org.briarproject.briar.desktop.introduction.IntroductionViewModel$makeIntroduction$1.invoke(IntroductionViewModel.kt:74)
at org.briarproject.briar.desktop.viewmodel.DbViewModel$runOnDbThread$1.invoke(DbViewModel.kt:29)
at org.briarproject.briar.desktop.viewmodel.DbViewModel$runOnDbThread$1.invoke(DbViewModel.kt:26)
at org.briarproject.briar.desktop.threading.BriarExecutorsImpl.onDbThread$lambda-0(BriarExecutorsImpl.kt:15)
at org.briarproject.bramble.TimeLoggingExecutor.lambda$execute$0(TimeLoggingExecutor.java:35)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:832)
```
where I read:
```java
@Override
public Message encodeRequestMessage(GroupId contactGroupId, long timestamp,
@Nullable MessageId previousMessageId, Author author,
@Nullable String text) {
if (text != null && text.isEmpty()) {
throw new IllegalArgumentException();
}
BdfList body = BdfList.of(
REQUEST.getValue(),
previousMessageId,
clientHelper.toList(author),
text
);
return createMessage(contactGroupId, timestamp, body);
}
```
We copied from Android that the message is optional, and I just confirmed it is optional there, however, I don't know how. Maybe we replace a `null` message with an empty string there.
issue