How to use the inferno-shared.isNullOrUndef function in inferno-shared

toArray: function (children) {
    if (isNullOrUndef(children)) {
      return [];
    }
    // We need to flatten arrays here,
    // because React does it also and application level code might depend on that behavior
    if (isArray(children)) {
      const result = [];

      flatten(children, result);

      return result;
    }
    return ARR.concat(children);
  }
};

if (isString(className)) {
      renderedString += ` class="${escapeText(className)}"`;
    } else if (isNumber(className)) {
      renderedString += ` class="${className}"`;
    }

    if (!isNull(props)) {
      for (const prop in props) {
        const value = props[prop];

        switch (prop) {
          case 'dangerouslySetInnerHTML':
            html = value.__html;
            break;
          case 'style':
            if (!isNullOrUndef(props.style)) {
              renderedString += ` style="${renderStylesToString(props.style)}"`;
            }
            break;
          case 'children':
          case 'className':
            // Ignore
            break;
          case 'defaultValue':
            // Use default values if normal values are not present
            if (!props.value) {
              renderedString += ` value="${isString(value) ? escapeText(value) : value}"`;
            }
            break;
          case 'defaultChecked':
            // Use default values if normal values are not present
            if (!props.checked) {

toArray(children: Array): Array {
    if (isNullOrUndef(children)) {
      return [];
    }
    // We need to flatten arrays here,
    // because React does it also and application level code might depend on that behavior
    if (isArray(children)) {
      const result = [];

      flatten(children, result);

      return result;
    }
    return ARR.concat(children);
  }
};

if (isString(className)) {
      renderedString += ` class="${escapeText(className)}"`;
    } else if (isNumber(className)) {
      renderedString += ` class="${className}"`;
    }

    if (!isNull(props)) {
      for (const prop in props) {
        const value = props[prop];

        switch (prop) {
          case 'dangerouslySetInnerHTML':
            html = value.__html;
            break;
          case 'style':
            if (!isNullOrUndef(props.style)) {
              renderedString += ` style="${renderStylesToString(props.style)}"`;
            }
            break;
          case 'children':
          case 'className':
            // Ignore
            break;
          case 'defaultValue':
            // Use default values if normal values are not present
            if (!props.value) {
              renderedString += ` value="${isString(value) ? escapeText(value) : value}"`;
            }
            break;
          case 'defaultChecked':
            // Use default values if normal values are not present
            if (!props.checked) {

options.createVNode = (vNode: VNode) => {
  const children = vNode.children as any;
  let props: any = vNode.props;

  if (isNullOrUndef(props)) {
    props = vNode.props = {};
  }

  // React supports iterable children, in addition to Array-like
  if (hasSymbolSupport && !isNull(children) && typeof children === 'object' && !isArray(children) && isFunction(children[symbolIterator])) {
    vNode.children = iterableToArray(children[symbolIterator]());
  }

  if (!isNullOrUndef(children) && isNullOrUndef(props.children)) {
    props.children = children;
  }
  if (vNode.flags & VNodeFlags.Component) {
    if (isString(vNode.type)) {
      vNode.flags = getFlagsForElementVnode(vNode.type as string);
      if (props) {
        normalizeProps(vNode);
      }
    }
  }

  const flags = vNode.flags;

  if (flags & VNodeFlags.FormElement) {
    normalizeFormProps(vNode.type, props);
  }

if (isString(className)) {
        renderedString += ` class="${escapeText(className)}"`;
      } else if (isNumber(className)) {
        renderedString += ` class="${className}"`;
      }

      if (!isNull(props)) {
        for (const prop in props) {
          const value = props[prop];

          switch (prop) {
            case 'dangerouslySetInnerHTML':
              html = value.__html;
              break;
            case 'style':
              if (!isNullOrUndef(props.style)) {
                renderedString += ` style="${renderStylesToString(props.style)}"`;
              }
              break;
            case 'children':
            case 'className':
              // Ignore
              break;
            case 'defaultValue':
              // Use default values if normal values are not present
              if (!props.value) {
                renderedString += ` value="${isString(value) ? escapeText(value) : value}"`;
              }
              break;
            case 'defaultChecked':
              // Use default values if normal values are not present
              if (!props.checked) {

function verifyKeys(vNodes) {
      if (Array.isArray(vNodes)) {
        const keyValues = vNodes.map(function(vnode) {
          return vnode.key;
        });
        const isDuplicate = keyValues.some(function(item, idx) {
          return keyValues.indexOf(item) !== idx;
        });

        expect(isDuplicate).toEqual(false);

        for (let i = 0; i < vNodes.length; i++) {
          verifyKeys(vNodes[i].children);
        }
      } else if (!isNullOrUndef(vNodes) && !!vNodes.flags) {
        verifyKeys(vNodes.children);
      }
    }

isSVG = isSVG || (flags & VNodeFlags.SvgElement) > 0;
  if (dom.nodeType !== 1 || dom.tagName.toLowerCase() !== vNode.type) {
    if (process.env.NODE_ENV !== 'production') {
      warning("Inferno hydration: Server-side markup doesn't match client-side markup");
    }
    _ME(vNode, null, context, isSVG, null, lifecycle);
    parentDOM.replaceChild(vNode.dom as Element, dom);
  } else {
    vNode.dom = dom;

    hydrateChildren(vNode, dom, dom.firstChild, context, isSVG, lifecycle);

    if (!isNull(props)) {
      _MP(vNode, flags, props, dom, isSVG);
    }
    if (isNullOrUndef(className)) {
      if (dom.className !== '') {
        dom.removeAttribute('class');
      }
    } else if (isSVG) {
      dom.setAttribute('class', className);
    } else {
      dom.className = className;
    }
    _MR(ref, dom, lifecycle);
  }

  return vNode.dom;
}