code: public PropertiesBuilder set(String propertyName, String propertyValue) {
      getProperties().setProperty(propertyName, propertyValue);
      return this;
    }
docs: Sets the named property to the given value.
  
  @param propertyName the name of the property to set.
  @param propertyValue the value to assign to the property.
  @return a reference to this builder.
  @see java.util.Properties#setProperty(String, String)
  @see #getProperties()