运行下面的代码时出现空指针异常：

public class Engine{

    private String name = null;
    private Mercedes m = null;

    private Engine() {

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Mercedes getM() {
        return m;
    }

    public void setM(Mercedes m) {
        this.m = m;
    }

    public static EngineBuilder builder() {
        return new EngineBuilder();
    }

    public static class EngineBuilder {
        private Engine e = null;

        public EngineBuilder builder() {
            e = new Engine();
            return this;
        }

        public Engine build() {
            return this.e;
        }

        public EngineBuilder setName(String name) {
            this.e.setName(name);
            return this;
        }

        public EngineBuilder setM(Mercedes m) {
            this.e.setM(m);
            return this;
        }

    }
    public static void main(String[] args) {
        EngineBuilder builder = Engine.builder();
        builder.setName("test");
                
        Engine e = builder.build();

    }
}
}

我希望Builder模式可以工作，但我得到了
线程“main”中出现异常java.lang.NullPointerException：无法调用“Engine.setName（String）”，因为“this.e”为空