[preact][mobx 5.13] TypeError: Cannot read property 'get' of undefined

[gganster]

Hi,
I've this error and I don't know how to solve it:
Uncaught TypeError: Cannot read property 'get' of undefined mobx.module.js.618

var computedDecorator = createPropDecorator(false, function (instance, propertyName, descriptor, decoratorTarget, decoratorArgs) { HERE -> var get = descriptor.get, set = descriptor.set; // initialValue is the descriptor for get / set props // Optimization: faster on decorator target or instance? Assuming target // Optimization: find out if declaring on instance isn't just faster. (also makes the property descriptor simpler). But, more memory usage.. // Forcing instance now, fixes hot reloadig issues on React Native: var options = decoratorArgs[0] || {}; asObservableObject(instance).addComputedProp(instance, propertyName, __assign({ get: get, set: set, context: instance }, options)); });

I'm using preact with mobx/mobx-preact: my package.json:
{ "name": "React-in-WP", "version": "1.0.0", "license": "MIT", "main": "src/index.js", "scripts": { "dev": "cross-env BABEL_ENV=default webpack --watch", "build": "cross-env BABEL_ENV=default NODE_ENV=production webpack -p" }, "devDependencies": { "@babel/core": "^7.5.5", "@babel/preset-env": "^7.5.5", "@wordpress/babel-preset-default": "^1.2.0", "autoprefixer": "^9.6.1", "babel-core": "^6.26.3", "babel-eslint": "^8.2.3", "babel-loader": "^7.1.4", "babel-plugin-transform-class-properties": "^6.24.1", "babel-plugin-transform-react-jsx": "^6.24.1", "classnames": "^2.2.6", "cross-env": "^5.1.5", "css-loader": "^3.1.0", "eslint": "^4.19.1", "extract-text-webpack-plugin": "^3.0.2", "mobx": "^5.13.0", "mobx-preact": "^3.0.0", "node-sass": "^4.9.0", "postcss-loader": "^2.1.5", "preact-places-autocomplete": "0.0.3", "preact-router": "^2.6.1", "raw-loader": "^0.5.1", "react": "^16.8.6", "sass-loader": "^6.0.7", "style-loader": "^0.19.1", "webpack": "^3.0.0", "webpack-cli": "^3.3.6" }, "dependencies": { "preact": "^8.4.2", "run-script": "^0.1.1" } }

and my babel.rc:
{ "plugins": [ ["transform-react-jsx", { "pragma": "h" }], "transform-class-properties" ] }
thanks

sorry for the indent, I don't know why github does not display my indentation. repo https://github.com/zoraneus/preact-mobx-reproduction-err

I have tried to put it in code sandbox but the error does not occur.