code: public void setDouble(final String propertyName, final double value) {
          if (propertyName == null) {
              throw new NullPointerException("propertyName must not be null.");
          }
          Integer index = propertyMap.get(propertyName);
          if (index == null) {
              throw new IllegalArgumentException("non existent property: '"
                      + propertyName + "'.");
          }
          this.data[index] = new double[]{value};
      }
docs: Sets the value of a property-list.
  If the property is a list, the list will be set to a single entry.
  @param propertyName Name of the property to set.
  @param value Value to set for that property.
  @throws NullPointerException if {@code propertyName} is {@code null}.
  @throws IllegalArgumentException if the element type does not have
  a property with the given name.