public static MethodCallExpression createGetAtMethodCall(Expression expression, String key) {
    return createMethodCall(expression, GET_AT_METHOD_NAME, new ConstantExpression(key));
  }
Turns an argument list obtained from AstUtil.getArguments() into an Object[] array
suitable to be passed to InvokerHelper or SpockRuntime. The main challenge is
to handle SpreadExpression's correctly.
spock-core/src/main/java/org/spockframework/compiler/AstUtil.java