server ram allocation in mac

Hi there,

I'm trying to start a moded server and I realised I would need to allocate more ram to have it run smoothly. I have followed other people's steps but I can't seem to make it work. The server by itself (no additional ram allocation) is functional. I get the following error when running the ram allocation script:

A problem occurred running the Server launcher.java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:70)
    at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:34)
Caused by: java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader 'bootstrap')
    at net.minecraft.launchwrapper.Launch.<init>(Launch.java:34)
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
    ... 6 more

my server_start.sh:

#!/bin/bash
cd "$(dirname "$0")"
exec java -Xms3G -Xmx3G -jar forge-1.12.2-14.23.5.2854.jar nogui

my java -version ooutput:

java version "14.0.1" 2020-04-14
Java(TM) SE Runtime Environment (build 14.0.1+7)
Java HotSpot(TM) 64-Bit Server VM (build 14.0.1+7, mixed mode, sharing)

Forge server: 1.12.2-14.23.5.2854

Thank you  in advance.