src/vs/platform/contextkey/common/contextkey.ts/ContextKeyDefinedExpr/create
class ContextKeyDefinedExpr:	public static create(key: string): ContextKeyExpression {
		const staticValue = STATIC_VALUES.get(key);
		if (typeof staticValue === 'boolean') {
			return staticValue ? ContextKeyTrueExpr.INSTANCE : ContextKeyFalseExpr.INSTANCE;
		}
		return new ContextKeyDefinedExpr(key);
	}