public String value() {
        return value;
    }
Returns the value of this string. Same as {@link #getValue()}
since the value of this node is a String (but implementations
in other {@link LeafNode} subclasses differ).

@return the string representation of this StringNode, or null if
        the value is explicitly set to null
config-lib/src/main/java/com/yahoo/config/StringNode.java