docs: public void override(String key, String value) {
          if(value==null || value.length()==0) {
              remove(key);
              return;
          }
  
          int idx = key.indexOf('+');
          if(idx>0) {
              String realKey = key.substring(0,idx);
              String v = get(realKey);
              if(v==null) v=value;
              else {
                  // we might be handling environment variables for a agent that can have different path separator
                  // than the master, so the following is an attempt to get it right.
                  // it's still more error prone that I'd like.
                  char ch = platform==null ? File.pathSeparatorChar : platform.pathSeparator;
                  v=value+ch+v;
              }
              put(realKey,v);
              return;
          }
  
          put(key,value);
      }