Custom GUI compiling problem with Input slots

Hello, I have an issue with GUIs : adding input slots either from a custom inventory than from one inherited from a block always gets me the same error.

Here is the gradle.log :

C:\Pylo\MCreator179\forge\build\sources\main\java\mod\mcreator\mcreator_testGUI.java:100: error: cannot find symbol
                        mcreator_null.executeProcedure(dependencies);
                        ^
  symbol: variable mcreator_null
C:\Pylo\MCreator179\forge\build\sources\main\java\mod\mcreator\mcreator_testGUI.java:122: error: cannot find symbol
                        mcreator_null.executeProcedure(dependencies);
                        ^
  symbol: variable mcreator_null
C:\Pylo\MCreator179\forge\build\sources\main\java\mod\mcreator\mcreator_testGUI.java:144: error: cannot find symbol
                        mcreator_null.executeProcedure(dependencies);
                        ^
  symbol: variable mcreator_null
C:\Pylo\MCreator179\forge\build\sources\main\java\mod\mcreator\mcreator_testGUI.java:166: error: cannot find symbol
                        mcreator_null.executeProcedure(dependencies);
                        ^
  symbol: variable mcreator_null
C:\Pylo\MCreator179\forge\build\sources\main\java\mod\mcreator\mcreator_testGUI.java:188: error: cannot find symbol
                        mcreator_null.executeProcedure(dependencies);
                        ^
  symbol: variable mcreator_null
C:\Pylo\MCreator179\forge\build\sources\main\java\mod\mcreator\mcreator_testGUI.java:210: error: cannot find symbol
                        mcreator_null.executeProcedure(dependencies);
                        ^
  symbol: variable mcreator_null
C:\Pylo\MCreator179\forge\build\sources\main\java\mod\mcreator\mcreator_testGUI.java:232: error: cannot find symbol
                        mcreator_null.executeProcedure(dependencies);
                        ^
  symbol: variable mcreator_null
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
7 errors

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed; see the compiler error output for details.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

I've put the problematic workspace(litteraly) in the attachments and I hope you'll see what's wrong here, thank you in advance !