Error during javadoc generation

Hi guys,

I am using gradle for my Vaadin based project and when I execute the javadoc task I get the following error :

/home/anthony/.gradle/caches/modules-2/files-2.1/com.vaadin/vaadin/6.8.13/e14ce1e652012b9435e720842c10ddbd9ea0ce2d/vaadin-6.8.13.jar(com/vaadin/ui/ error: cannot access Paintable import com.vaadin.terminal.gwt.client.Paintable; ^ bad source file: /home/anthony/.gradle/caches/modules-2/files-2.1/com.vaadin/vaadin/6.8.13/e14ce1e652012b9435e720842c10ddbd9ea0ce2d/vaadin-6.8.13.jar(com/vaadin/terminal/gwt/client/ file does not contain class com.vaadin.terminal.gwt.client.Paintable Please remove or make sure it appears in the correct subdirectory of the sourcepath. 1 error Any idea on how to fix this ?

Thank you