Continuing to say hello when nobody is there is repetitive and annoying.
You could take it in a couple of directions, like unwritten rules between friends or you could go with society at large.
So, either way, it works out.
Call the person to go deeper.
If you take a second to read your text message out loud, you will quickly be able to figure out whether it should be sent.
How to not be a boring texter and keep anyone interested ] 5 Bring up details from past conversations.
If it isn't going anywhere, don't let it continue.
If not, just flip to another topic.