I want to add a JGoodies separator. So, I add JComponent to the palette and drop it to my form.
I set customCreate to true.
I add this code below:

private void createUIComponents() {
    woSeparator = DefaultComponentFactory.getInstance().createSeparator("Work Order");
}

Then, I try to preview the form. InstantiationError is thrown:

Exception in thread "main" java.lang.InstantiationError: javax.swing.JComponent
	at FormPreviewFrame.$$$setupUI$$$(FormPreviewFrame.java)
	at FormPreviewFrame.<init>(FormPreviewFrame.java:69)
	at FormPreviewFrame.main(FormPreviewFrame.java:15)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:90)

I think IDEA tried to instantiate the class although the class is abstract. It should be better to skip abstract custom created components.

Issue was resolved