code: public String getAttribute(String name)
    {
      Params.notNullOrEmpty(name, "Attribute name");
      return attributes.get(name);
    }
docs: Get attribute value or null if there is no attribute with requested name. An existing attribute value cannot ever
  be empty or null so if this method returns null is for missing attribute.
  
  @param name attribute name.
  @return attribute value or null if named attribute not found.
  @throws IllegalArgumentException if <code>name</code> argument is null or empty.