Minecraft plugin error message?

I'm programming my own Minecraft plugin, but whenever I start my localhost server I get this error message:

Error occurred while enabling PROFI v1 (Is it up to date?)

java.lang.NullPointerException

at me.verkaufecannabis.helloworld.Main.onEnable (Main.java:35) ~ [?:?]

at org.bukkit.plugin.java.JavaPlugin.setEnabled (JavaPlugin.java:321) ~ [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin (JavaPluginLoader.java:340) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at org.bukkit.plugin.SimplePluginManager.enablePlugin (SimplePluginManager.java:405) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at org.bukkit.craftbukkit.v1_8_R3.CraftServer.loadPlugin (CraftServer.java:357) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at org.bukkit.craftbukkit.v1_8_R3.CraftServer.enablePlugins (CraftServer.java:317) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at net.minecraft.server.v1_8_R3.MinecraftServer.s (MinecraftServer.java:414) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at net.minecraft.server.v1_8_R3.MinecraftServer.k (MinecraftServer.java:378) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at net.minecraft.server.v1_8_R3.MinecraftServer.a (MinecraftServer.java:333) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at net.minecraft.server.v1_8_R3.DedicatedServer.init (DedicatedServer.java:263) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at net.minecraft.server.v1_8_R3.MinecraftServer.run (MinecraftServer.java:525) [Spigot1.8.8.jar: git-Spigot-21fe707-e1ebe52]

at java.lang.Thread.run (Thread.java:748) [?: 1.8.0_292]

in addition to all of the files from Spigot it says:
The JAR file "path" has no source attachment.
You can attach the source by clicking Attach Source below:

what do I have to attach there?

We can't help you without the code, and I would strongly recommend that you learn the basics of Java first before you start with Spigot, as solving an NPE (NullPointerException), for example, is definitely part of these basics.

First of all, thanks for the quick answer and yes, I should learn more java first, but it would still be nice if you somehow manage to answer my second question (The JAR file "path" has no source attachment.
You can attach the source by clicking Attach Source below:
what exactly should I add?)

That sounds like an error that occurs when building the plugin, since I use Gradle for this I can't help you much

And to my first question I noticed how stupid I was because I just saved something in another folder but forgot it

Ok thanks anyway

Java.lang.NullPointerException
at me.verkaufecannabis.helloworld.Main.onEnable (Main.java:35) ~ [?:?]

The error occurs in your Main.java in line 35. Could you just post what's on this line?