Copy the Hangul Filler character to send empty messages, hide your About status, or prank friends.
If you press the Spacebar and hit Send, WhatsApp disables the button. This is because WhatsApp automatically trims standard whitespace (ASCII 32). However, you can bypass this using the Hangul Filler (U+3164).
Because U+3164 is technically a "letter" in the Korean alphabet, WhatsApp allows it to be sent. Since it has no visual design, the result is an invisible message.
You can use this tool to create the famous "Read More" joke. By pasting the invisible character multiple times (or hitting "Enter" between them), you can create a very long message that is completely empty.
Want a ghost profile? You can make your "About" section blank too.