NPE occurs when calling BlockData#.getHalf()

Caused by: java.lang.IllegalArgumentException: value already present: TOP
at com.google.common.collect.HashBiMap.put(HashBiMap.java:287) ~[X.jar:g
it-Spigot-a85f7ec-5870145]
at com.google.common.collect.HashBiMap.put(HashBiMap.java:262) ~[X.jar:g
it-Spigot-a85f7ec-5870145]
at org.bukkit.craftbukkit.v1_13_R1.block.data.CraftBlockData.toBukkit(Cr
aftBlockData.java:114) ~[X.jar:git-Spigot-a85f7ec-5870145]
at org.bukkit.craftbukkit.v1_13_R1.block.data.CraftBlockData.get(CraftBl
ockData.java:57) ~[X.jar:git-Spigot-a85f7ec-5870145]
at org.bukkit.craftbukkit.v1_13_R1.block.impl.CraftStairs.getHalf(CraftS
tairs.java:36) ~[X.jar:git-Spigot-a85f7ec-5870145]

Also make sure you include the full output of /version in your report. Please copy and paste this statement to the bottom of your report to indicate that you have read and understood it.