Exception:

java.lang.IllegalArgumentException: Cannot set property BlockStateEnum{name=half, clazz=class net.minecraft.server.v1_13_R1.BlockPropertyHalf, values=[top, bottom]} to lower on minecraft:acacia_stairs, it is not an allowed value
at net.minecraft.server.v1_13_R1.BlockDataAbstract.set(SourceFile:114) ~[spigot.jar:git-Spigot-0b44fa0-19ff43d]
at org.bukkit.craftbukkit.v1_13_R1.block.data.CraftBlockData.set(CraftBlockData.java:89) ~[spigot.jar:git-Spigot-0b44fa0-19ff43d]
at org.bukkit.craftbukkit.v1_13_R1.block.impl.CraftStairs.setHalf(CraftStairs.java:41) ~[spigot.jar:git-Spigot-0b44fa0-19ff43d]

Test code:

public void onEnable() {
 Door door = ((Door) Material.ACACIA_DOOR.createBlockData());
 door.setHalf(door.getHalf());
 Stairs stairs = ((Stairs) Material.ACACIA_STAIRS.createBlockData());
 stairs.setHalf(stairs.getHalf());
}