When doing something like this:

player.sendSignChange(sign.getLocation(), sign.getLines(), sign.getColor() == null ? DyeColor.BLACK : sign.getColor());

I get the following exception - looks like it tries to update the sign in the world (is should not do that, just send the sign to the client):

[16:51:31] [Server thread/WARN]: [InSigns] Task #16 for InSigns v2.7.1-SNAPSHOT generated an exception
java.lang.NullPointerException: null
at net.minecraft.server.v1_14_R1.TileEntity.getBlock(TileEntity.java:132) ~[spigot-1.14.3.jar:git-Spigot-935adb3-bf0ea33]
at net.minecraft.server.v1_14_R1.TileEntitySign.setColor(TileEntitySign.java:181) ~[spigot-1.14.3.jar:git-Spigot-935adb3-bf0ea33]
at org.bukkit.craftbukkit.v1_14_R1.entity.CraftPlayer.sendSignChange(CraftPlayer.java:553) ~[spigot-1.14.3.jar:git-Spigot-935adb3-bf0ea33]