Build Failed when making gui

Status
Works as designed
Issue description

Whenever I go to make a GUI, it fails to build and i'm not sure why?

 

:clean
:deobfCompileDummyTask
:deobfProvidedDummyTask
:sourceApiJava
:compileApiJava UP-TO-DATE
:processApiResources UP-TO-DATE
:apiClasses UP-TO-DATE
:sourceMainJava
C:\Pylo\MCreator179\forge\build\sources\main\java\mod\mcreator\mcreator_blockGui.java:79: error: cannot find symbol
         if (ent != null && (ent instanceof mcreator_demo.TileEntityCustom))
                                                         ^
  symbol:   class TileEntityCustom
  location: class mcreator_demo
1 error
:compileJava FAILED
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.
BUILD FAILED
Total time: 15.775 secs
C:\Pylo\MCreator179\forge>
Task completed with return code 0 in 16431 milliseconds

Issue comments

If you bind a GUI to a block, a block needs to have an inventory. Open editor for the block called Demo and enable the inventory/container of this block in the editor.