code: public static <A extends Comparable<? super A>> ComparableExpression<A> avg(CollectionExpression<?,A> col) {
          return Expressions.comparableOperation((Class) col.getParameter(0), Ops.QuantOps.AVG_IN_COL, (Expression<?>) col);
      }
docs: Create a avg(col) expression
  
  @param col collection
  @return avg(col)