[MONDRIAN-1616]  NPE could be thrown in ValidMeasure when role restrictions prevent access to a virtual cube's base cubes.
(cherry picked from commit 08724bc)
[MONDRIAN-1616] Switched to using Collections.singletonList.
(cherry picked from commit c1456b7)
Merge pull request #121 from mkambol/3.5mondrian1616

[MONDRIAN-1616]  NPE could be thrown in ValidMeasure when role restrictions prevent access to a virtual cube's base cubes.