Steps to reproduce:

- Create a JavaFX Desktop Business Application
- Drag a Label component from the Controls section of the Palette and drop it into the Design area. 

-  In the Properties window, click the Layout Info icon Layout info icon in the toolbar

- Change the Min. Width property to 100
- Press enter

- Delete the value for the Min. Width property
- Build the project
-----------------------------------------------
Main.fx:16: incompatible types
found   : <nulltype>
required: Number
        minWidth: null
1 error
-----------------------------------------------

The source code is:
-----------------------------------------------
    def __layoutInfo_label: javafx.scene.layout.LayoutInfo = javafx.scene.layout.LayoutInfo {
        minWidth: null
    }
-----------------------------------------------