Fatal error from calling firstChild() of TokenNode in IdentifierNameTrait

[phenaproxima]

DMU is getting fatals from this method of IdentifierNameTrait:

  /**
   * Set the identifier name of this node.
   *
   * @param string $name
   *   New name.
   * @return $this
   */
  public function setName($name) {
    /** @var TokenNode $identifier */
    $identifier = $this->name->firstChild();
    $identifier->setText($name);
    return $this;
  }

TokenNode hasn't got a firstChild() method since it doesn't implement ParentNodeInterface. So this fatal results:

Call to undefined method Pharborist\TokenNode::firstChild() in /path/to/pharborist/src/Namespaces/IdentifierNameTrait.php, line 40