Gama Server GUI: error when loading a model

[leonsi7]

Describe the bug
I'm working with Gama Server GUI. I wrote a simple models which works perfectly with Gama Server 1.9.2 (loading, and running) and which creates a Gama Server Error with Gama 1.9.3. Actually, this models creates an exception in Gama Server and does not send a weboscket message about the error/exception

To Reproduce
Please use my newly developed NodeJS server here. Follow the installation intructions and load /models/model1.gaml. You can try it with gama server 1.9.2 and gama server GUI to compare the results.

The exception returned by Gama Server GUI in the console is:

java.lang.NullPointerException: Cannot invoke "Object.toString()" because the return value of "msi.gama.util.IMap.get(Object)" is null
	at msi.gama.runtime.server.CommandExecutor.process(CommandExecutor.java:112)
	at msi.gama.runtime.server.CommandExecutor.lambda$0(CommandExecutor.java:66)
	at java.base/java.lang.Thread.run(Thread.java:833)

Expected behavior
The simulation must normally be lauched correcly like with Gama server 1.9.2

Desktop (please complete the following information):

OS: macOS
GAMA version: Gama Server GUI 1.9.3