_document.js error from ctx.renderPage().

Hi,
While trying to apply Material-ui styles into a Next app, I am getting error from the _document.js file, in the ctx.renderPage( ) function
Below is error log output-
----->
Error: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in, or you might have mixed up default and named imports.

The error results from this function -->
ctx.renderPage = () =>
originalRenderPage({
enhanceApp: (App) =>
function EnhanceApp(props) {
return ;
},

I would grateful for all useful advice
Thanks