When one of the vectors is a zero vector:
length(u + 0) <= length(u) + length(0)
Add the zero matrix ( 0, 0 )T to the matrix ( 4, 3 )T. If (0, 0)T represents a displacement vector, it means do nothing to change position.
Now consider what this might mean: add the vector (1, 2)T to the point (4, 4)T.
If you think that makes sense, then do the calculation. What type of object is the result?