Worked around possible bug in luassert

assert.Nil results in the following error:
luassert/assertions.lua:109: bad argument #2 to 'insert' (position out of bounds)
As a work-aroung, assert.equals(x, nil) is used instead
Constructors are now inherrited like other methods
Merge branch 'master' of https://github.com/Pezzer13/LuaOO