Fix warning in Gradle build

For some reason this caused the build to fail on the tools server with:

Ambiguous method overloading for method java.io.File#<init>.
  Cannot resolve which method to invoke for [null, class java.lang.String] due to overlapping prototypes between:
        [class java.lang.String, class java.lang.String]
        [class java.io.File, class java.lang.String]

Change-Id: Ib32ef1f0ffbec5c142ea3f0e65e6076aa04eccb0