Tell us about your environment

• ESLint Version: 6.7.0
• Node Version: 12.13.1
• npm Version: 6.12.1

What parser (default, Babel-ESLint, etc.) are you using? babel-eslint

Please show your full configuration:

// .eslintrc.basic.js
module.exports = {
  plugins: [],

  extends: [
    'eslint:all'
  ],

  parser: 'espree',

  parserOptions: {
    ecmaVersion: 7,
    sourceType: 'module'
  },

  settings: {},

  env: {
    es6: true
  },

  rules: {
    'camelcase': ['warn', {properties: 'never'}]
  }
}

// .eslintrc.babel.js
let _basic = require('./.eslintrc.basic');

module.exports = {
  parser: 'babel-eslint',

  parserOptions: {
    sourceType: 'module'
  },

  plugins: [
    'babel'
  ],

  rules: {
    camelcase: 'off',
    'babel/camelcase': _basic.rules.camelcase
  }
};

// .eslintrc.js
module.exports: {
  extends: [
    './.eslintrc.basic.js',
    './.eslintrc.babel.js'
  ]
}

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

N/A

N/A

What did you expect to happen?

I expected no errors.

What actually happened? Please include the actual, raw output from ESLint.

	Configuration for rule "babel/camelcase" is invalid:
	Value {"properties":"never","ignoreDestructuring":false,"ignoreImports":false} should NOT have additional properties.

This happens because of #12528 adding ignoreImports with default value failse, and because the defaults of camelcase are merged into the same object in .eslintrc.basic.js:rules.camelcase, which is also the same reference in .eslintrc.babel.js:rules.@babel/camelcase.

Are you willing to submit a pull request to fix this bug?

Sure.