code: public static ModelNode setPossibleExpression(ModelNode node, String name, String value) {
          if (value != null) {
              if (value.contains("${")) {
                  return node.get(name).set(new ValueExpression(value));
              } else {
                  return node.get(name).set(value);
              }
          } else {
              return node.get(name).clear();
          }
      }
docs: This sets the given node's named attribute to the given value. If the value
  appears to be an expression (that is, contains "${" somewhere in it), this will
  set the value as an expression on the node.
  
  @param node the node whose attribute is to be set
  @param name the name of the attribute whose value is to be set
  @param value the value, possibly an expression
  
  @return returns the node