code: @NonNull
      public static Expression power(@NonNull Expression base, @NonNull Expression exponent) {
          if (base == null || exponent == null) {
              throw new IllegalArgumentException("base or exponent cannot be null.");
          }
          return new Expression.FunctionExpression("POWER()", Arrays.asList(base, exponent));
      }
docs: Creates a POWER(base, exponent) function that returns the value of the given base
  expression power the given exponent expression.
  
  @param base     The base expression.
  @param exponent The exponent expression.
  @return The POWER(base, exponent) function.