PostCSS custom plugin - TypeError: Cannot read property '_autoprefixerPrefix' of undefined - postcss

Question

I am developing a postCSS plugin, in which, you can use custom atRules for bem classes. Here is the demo:
https://astexplorer.net/#/gist/147ddf920699ac24b690a05f8f8da8f1/15aeb3c85224f3d20de47a1774c25f330ed9d16e
It works fine by its own, but when using it in a project alongside with autoprefixer, the autoprefixer yelds an error: TypeError: Cannot read property '_autoprefixerPrefix' of undefined.
Any reason you can think of or any way to debug this maybe?
You can also copy paste all the code below in npm runkit to get the exact error.
const autoprefixer = require("autoprefixer");
const postcss = require('postcss');
const css = `
#b BaseButton {
#apply shadow-neon-default;
#apply rounded-full;
box: horizontal;
position: relative;
overflow: hidden;
user-select: none;
&:hover {
#apply shadow-neon-less;
}
&:active {
#apply shadow-neon-inset;
}
#is faded {
opacity: 0.8;
}
}
`;
const toTitleCase = (str) => {
return str.replace(/\w\S*/g, function(txt) {
return txt.charAt(0).toUpperCase() + txt.substr(1).toLowerCase();
});
};
const createRule = (selector, { source, nodes, raws }) => {
return postcss.rule({
selector,
source,
nodes,
raws
});
};
const recycleBin = {
element: [],
modifier: [],
is: [],
when: [],
whenIs: []
};
const emptyRecycleBin = (type) => {
recycleBin[type].forEach((rule) => {
rule.remove();
});
};
const willInsert = [];
const insertEverything = (root) => {
Object.values(willInsert).forEach((insertInstruction) => {
insertInstruction.rules.reverse().forEach((rule) => {
root.insertAfter(insertInstruction.baseRule, rule);
});
insertInstruction.baseRule.remove();
});
};
let newBlock = null;
const processBlocks = (container, next) => {
container.walkAtRules(/^block$|^b$/gi, (blockAtRule) => {
willInsert[`.${blockAtRule.params}`] = {
baseRule: blockAtRule,
rules: []
};
newBlock = createRule(`.${blockAtRule.params}`, blockAtRule);
willInsert[`.${blockAtRule.params}`].rules.push(newBlock);
next(newBlock);
});
};
const processElements = (container, blockName, next) => {
container.walkAtRules(/^element$|^e$/gi, (elementAtRule) => {
const newElement = createRule(`${container.selector}__${elementAtRule.params}`, elementAtRule);
willInsert[blockName].rules.push(newElement);
recycleBin.element.push(elementAtRule);
next(newElement);
});
emptyRecycleBin('element');
};
const processModifier = (container, blockName) => {
container.walkAtRules(/^modifier$|^m$/gi, (modifierAtRule) => {
const newModifier = createRule(`${container.selector}--${modifierAtRule.params}`, modifierAtRule);
willInsert[blockName].rules.push(newModifier);
recycleBin.modifier.push(modifierAtRule);
});
emptyRecycleBin('modifier');
};
const processIs = (container, blockName) => {
container.walkAtRules('is', (isAtRule) => {
if (isAtRule.parent.name !== 'when') {
const newModifier = createRule(`${container.selector}--is${toTitleCase(isAtRule.params)}`, isAtRule);
willInsert[blockName].rules.push(newModifier);
recycleBin.is.push(isAtRule);
}
});
emptyRecycleBin('is');
};
const processWhen = (container, blockName, cb) => {
container.walkAtRules('when', (whenAtRule) => {
const newWhen = createRule(`[class*='${container.selector.substring(1)}--${whenAtRule.params}']`, whenAtRule);
willInsert[blockName].rules.push(newWhen);
newWhen.walkAtRules('is', (isAtRule) => {
const newIs = createRule(`${newWhen.selector.slice(0, -2)}:${isAtRule.params}']`, isAtRule);
willInsert[blockName].rules.push(newIs);
recycleBin.whenIs.push(isAtRule);
});
emptyRecycleBin('whenIs');
recycleBin.when.push(whenAtRule);
});
emptyRecycleBin('when');
};
const process = (root) => {
processBlocks(root, (processedBlock) => {
processElements(processedBlock, processedBlock.selector, (processedElement) => {
processModifier(processedElement, processedBlock.selector);
processIs(processedElement, processedBlock.selector);
processWhen(processedElement, processedBlock.selector);
});
processModifier(processedBlock, processedBlock.selector);
processIs(processedBlock, processedBlock.selector);
processWhen(processedBlock, processedBlock.selector);
insertEverything(root);
});
};
const bemmify = postcss.plugin('postcss-bem', (options = {}) => {
return (root) => {
process(root);
};
});
postcss([ bemmify, autoprefixer ]).process(css).then(result => {
result.warnings().forEach(warn => {
console.warn(warn.toString())
})
console.log(result.css)
});