[2.7.x] Functional components don't compile properly

[Tofandel]

Version

2.7.3

Reproduction link

github.com/Tofandel/vue-bug

(That issue cannot be reproduced on codesandbox)

Steps to reproduce

Use a functional component with both a static part and a dynamic part on vue 2.7.x

You can clone the reproduction, run yarn install and yarn serve
The page is not rendered, look at the error in the console

What is expected?

No error to be thrown

What is actually happening?

[Vue warn]: Error in render: "TypeError: _c is not a function"

---

I recently upgraded from 2.6.14 to 2.7.3

In vue 2.6.14

<template functional>
  <div :class="classes">
    <p>{{str}}</p>
    <span><a>Hi bug</a></span>
  </div>
</template>

<script>
export default {
  props: {
    classes: null,
    str: String
  }
}
</script>

Used to compile to:

var render = function (_h, _vm) {
    var _c = _vm._c
    return _c("div", {class: _vm.classes}, [
        _c("p", [_vm._v(_vm._s(_vm.str))]),
        _vm._m(0),
    ])
};
var staticRenderFns = [
    function (_h, _vm) {
        var _c = _vm._c
        return _c("span", [_c("a", [_vm._v("Hi bug")])])
    }
];

On vue 2.7.3 it compiles to:

var render = function render(_c, _vm) {
    return _c("div", {
        class: _vm.classes
    }, [_c("p", [_vm._v(_vm._s(_vm.str))]), _vm._m(0)]);
};
var staticRenderFns = [function (_c, _vm) {
    return _c("span", [_c("a", [_vm._v("Hi bug")])]);
}];

The first parameter of staticRenderFns is always null on both version, so it does seem obvious there is an issue in the compilation