src/vs/workbench/contrib/codeEditor/browser/languageConfigurationExtensionPoint.ts/LanguageConfigurationFileHandler/_extractValidBrackets
class LanguageConfigurationFileHandler:	private _extractValidBrackets(languageIdentifier: LanguageIdentifier, configuration: ILanguageConfiguration): CharacterPair[] | null {
		const source = configuration.brackets;
		if (typeof source === 'undefined') {
			return null;
		}
		if (!Array.isArray(source)) {
			console.warn(`[${languageIdentifier.language}]: language configuration: expected \`brackets\` to be an array.`);
			return null;
		}

		let result: CharacterPair[] | null = null;
		for (let i = 0, len = source.length; i < len; i++) {
			const pair = source[i];
			if (!isCharacterPair(pair)) {
				console.warn(`[${languageIdentifier.language}]: language configuration: expected \`brackets[${i}]\` to be an array of two strings.`);
				continue;
			}

			result = result || [];
			result.push(pair);
		}
		return result;
	}