code: public static Projection project(Projection... projection) {
          if (projection.length == 1) {
              return projection[0];
          } else {
              Projection x = new Projection(true);
              for (Projection p : projection) {
                  x.addToArray(p.toJson());
              }
              return x;
          }
      }
docs: <pre>
  [ projection ... ]
  </pre>