Missing env variables for runClient <=MC1.16.5

[Elec332]

On a clean project as per https://github.com/MinecraftForge/MDKExamples/blob/master/obfuscation/fg7/build.gradle

When attempting to runClient a project for any MC version <= 1.16.5 (e.g. MC 1.16.5 Forge 36.2.42) using java 8 SlimeLauncher complains about missing env variables. Example output:

> Task :runClient FAILED
Slime Launcher setup is up-to-date, took 317ms
Launching using main class: net.minecraftforge.userdev.LaunchTesting
2026-03-05 00:04:41,393 main WARN Advanced terminal features are not available in this environment
4 actionable tasks: 1 executed, 3 up-to-date
Exception in thread "main" java.lang.IllegalArgumentException: Environment variable 'assetDirectory' must be set to a valid path.
	at net.minecraftforge.userdev.LaunchTesting.main(LaunchTesting.java:62)
	at net.minecraftforge.launcher.Main$Launcher.run(Main.java:152)
	at net.minecraftforge.launcher.Main$Launcher.access$000(Main.java:138)
	at net.minecraftforge.launcher.Main.main(Main.java:49)
Something went wrong! Here is some debug info.
Args: [--main, net.minecraftforge.userdev.LaunchTesting, --cache, E:\Programming\.environment\.gradle\caches\minecraftforge\forgegradle\slime-launcher\cache\net\minecraftforge\forge\1.16.5-36.2.42, --metadata, E:\Programming\Local\Java\forge-FG7-test\.gradle\mavenizer\repo\net\minecraftforge\forge\1.16.5-36.2.42\forge-1.16.5-36.2.42-metadata.zip, --]
JVM Args: [-XX:+IgnoreUnrecognizedVMOptions, --add-exports=java.base/sun.security.util=ALL-UNNAMED, --add-exports=jdk.naming.dns/com.sun.jndi.dns=java.naming, --add-opens=java.base/java.util.jar=ALL-UNNAMED]
Environment:
	MOD_CLASSES: E:\Programming\Local\Java\forge-FG7-test\build\sourceSets\main;E:\Programming\Local\Java\forge-FG7-test\build\sourceSets\main
	MCP_MAPPINGS: official_1.16.5
	MCP_VERSION: 20210115.111550
	FORGE_VERSION: 36.2.42
	assetIndex: {asset_index}
	assetDirectory: {assets_root}
	nativesDirectory: {natives}
	FORGE_GROUP: net.minecraftforge
	target: fmluserdevclient
	MC_VERSION: 1.16.5
System:
	eventbus.api.strictRuntimeChecks: true
	forge.enabledGameTestNamespaces: examplemod
Options: SlimeLauncherOptionsImpl{name=client, mainClass=net.minecraftforge.userdev.LaunchTesting, args=[], jvmArgs=[-XX:+IgnoreUnrecognizedVMOptions, --add-exports=java.base/sun.security.util=ALL-UNNAMED, --add-exports=jdk.naming.dns/com.sun.jndi.dns=java.naming, --add-opens=java.base/java.util.jar=ALL-UNNAMED], classpath=[], minHeapSize=null, maxHeapSize=null, systemProperties={eventbus.api.strictRuntimeChecks=true, forge.enabledGameTestNamespaces=examplemod}, environment={MOD_CLASSES={source_roots}, MCP_MAPPINGS={mcp_mappings}, MCP_VERSION=20210115.111550, FORGE_VERSION=36.2.42, assetIndex={asset_index}, assetDirectory={assets_root}, nativesDirectory={natives}, FORGE_GROUP=net.minecraftforge, target=fmluserdevclient, MC_VERSION=1.16.5}, workingDir=E:\Programming\Local\Java\forge-FG7-test\run, client=false}