Please help, I started to make a plugin and in the cmd it said:

[17:28:24 ERROR]: Could not load 'plugins\CustomPlugin.jar' in folder 'plugins'
org.bukkit.plugin.InvalidDescriptionException: commands are of wrong type
{{ at org.bukkit.plugin.PluginDescriptionFile.loadMap(PluginDescriptionFile.java:917) ~[Spigot.jar:git-Spigot-0869666-03f1e37]}}
{{ at org.bukkit.plugin.PluginDescriptionFile.<init>(PluginDescriptionFile.java:226) ~[Spigot.jar:git-Spigot-0869666-03f1e37]}}
{{ at org.bukkit.plugin.java.JavaPluginLoader.getPluginDescription(JavaPluginLoader.java:157) ~[Spigot.jar:git-Spigot-0869666-03f1e37]}}
{{ at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:133) [Spigot.jar:git-Spigot-0869666-03f1e37]}}
{{ at org.bukkit.craftbukkit.v1_12_R1.CraftServer.loadPlugins(CraftServer.java:302) [Spigot.jar:git-Spigot-0869666-03f1e37]}}
{{ at net.minecraft.server.v1_12_R1.DedicatedServer.init(DedicatedServer.java:205) [Spigot.jar:git-Spigot-0869666-03f1e37]}}
{{ at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:544) [Spigot.jar:git-Spigot-0869666-03f1e37]}}
{{ at java.lang.Thread.run(Unknown Source) [?:1.8.0_121]}}
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to java.util.Map
{{ at org.bukkit.plugin.PluginDescriptionFile.loadMap(PluginDescriptionFile.java:899) ~[Spigot.jar:git-Spigot-0869666-03f1e37]}}

I have no idea what to do, please help