code: public void with(Properties source) {
      Assert.notNull(source, "Source properties cannot be null");
      String propertyName = getPropertyName();
      getProperties().setProperty(propertyName, source.getProperty(propertyName));
    }
docs: Sets the identified property with name to the value of the property from the given {@link Properties}.
  
  @param source {@link Properties} used as the source of the value for the named property to set.
  @throws IllegalArgumentException if source {@link Properties} are {@literal null}.
  @throws IllegalStateException if target {@link Properties} are {@literal null}.
  @see java.util.Properties#getProperty(String)
  @see java.util.Properties#setProperty(String, String)
  @see #getProperties()
  @see #getPropertyName()