Merge: Less null warnings in src/

Some small warning reductions while wandering in the source code of src/

Pull-Request: #1782
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --cc src/compiler/abstract_compiler.nit
Simple merge

diff --cc src/interpreter/naive_interpreter.nit
Simple merge

diff --cc src/model/mmodule.nit
Simple merge

diff --cc src/modelize/modelize_property.nit
Simple merge