Getting sign lines from block break event returns null

[tyhdefu]

In a break block event, I try to get the data of a sign, I check if its a wall sign, it is, so it continues, pastes all of the sign data into console:
[13:19:50 WARN] [test]: {"ContentVersion":1,"WorldUuid":"0e8d1aa1-f7db-411b-b732-7027b0444aa9","Position":{"X":549,"Y":82,"Z":-45},"BlockState":{"ContentVersion":2,"BlockState":"minecraft:wall_sign[facing=south]"},"UnsafeData":{"x":549,"Text4":"{\"text\":\"defutyh\"}","y":82,"Text3":"{\"text\":\"dirt 10\"}","z":-45,"Text2":"{\"text\":\"stone 1\"}","id":"minecraft:sign","Text1":"{\"text\":\"[Shop]\"}"}}

Yet when I try to retrieve the data using keys, it gives a no such element exception. I would expect it to return the first sign line to console.

for ( Transaction<BlockSnapshot> block : event.getTransactions())
{
    if (!block.getOriginal().getState().getType().equals(BlockTypes.WALL_SIGN))
    {
        continue;
    }
    logger.warn(DataFormats.JSON.write(block.getOriginal().toContainer()));
    logger.warn(block.getOriginal().get(Keys.SIGN_LINES).get().get(0).toPlain());
}

To reproduce:
Add this code to the block break event listener,
Go into the server and break a sign, should get an error in console.

SpongeVanilla 1.12.2

[JBYoshi]

I can reproduce this on SpongeForge RC3950.

[JBYoshi]

Will be fixed by #1905.