Updated RSPEC to remove example of a constant concatenated with an empty String, accordingly to SONARJAVA-2452. Concatenation of literals with empty string (or any String literal) is valid and will produce an optimized string when compiled into bytecode.
Removing string concatenation altogether from this rule because, as described in \https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.18.1 modern Java compilers can and do optimize string concatenation of primitive values. Furthermore concatenation can be effectively optimized by JIT and trying to be smart may circumvent these optimizations. See for example \http://openjdk.java.net/jeps/280 . Implemented in SONARJAVA-2481