code: public static boolean safeNavigationOperatorDefined(String nestedFieldName){
  		if(nestedFieldName.contains(SAFE_NAVIGATION_OPERATOR))
  			if(!nestedFieldName.startsWith(SAFE_NAVIGATION_OPERATOR))
  				//TODO standardizzare exception
  				throw new MappingException("Safe navigation operator must be the first symbol after dot notation");
  			else
  				return true;
  		
  		return false;
  	}
docs: It checks the presence of the elvis operator and how it is used.
  @param nestedFieldName field name to check
  @return true if is used an elvis operator, false otherwise, for all other cases a MappingException will be thrown