I called forge’s get item method in the command class of sponge, and there was an error.
The error is explicitly indicated by the code in the red box.
But sponge didn’t tell me more about it
Thats where your issue is, MCP makes development easier by renaming everything in minecraft to human readable names, however MCP can not convert it on the fly, therefore when you extract your jar MCP needs to be applied to it.
If you build your plugin through gradle then MCP will be applied. Assuming your using ForgeGradle to gain minecraft in your development enviroment, you should build your plugin using the following command.
gradle clean build
You can find the document for Sponge with ForgeGradle here
I can see that the imports were used. Im saying if those methods arnt ran when you were testing it, then no error would have been thrown as the code hasnt ran
Any and all classes from minecraft (as in net.minecraft) will cause a crash if not converted. So EntityMP will still cause the crash.
I personally dont know why it doesnt crash with that code if those methods are ran during runtime as by all accounts it should unless there is emulation going on