GodZza

void Update(){

    emissionRate += 1;

    ps.emission.rateOverTime = new ParticleSystem.MinMaxCurve(emissionRate);

}

        //     Script interface for the EmissionModule of a Particle System.
        public struct EmissionModule
        {
            public bool enabled { get; set; }            
            public MinMaxCurve rateOverTime { get; set; }            
            public float rateOverTimeMultiplier { get; set; }           
            public MinMaxCurve rateOverDistance { get; set; }           
            public float rateOverDistanceMultiplier { get; set; }
            public int burstCount { get; set; }
            public Burst GetBurst(int index);
            public int GetBursts(Burst[] bursts);
            public void SetBurst(int index, Burst burst);
            public void SetBursts(Burst[] bursts);
            public void SetBursts(Burst[] bursts, int size);
            // ... Obsolete ... ignore
        }

struct EmissionModule
{
    private int handle;
    public int rate;
    void SetRate(){
　     var ps = GetPsInCpp(handle);
        ps.rate = this.rate;      
    }
}

public class ParticleSystemController : MonoBehaviour
{
    [SerializeField]
    new ParticleSystem  particleSystem;

    [SerializeField]
    int emissionRate = 10;

    ParticleSystem.EmissionModule emissionModule;
    void Start(){
        //var rot = particleSystem.emission.rateOverTime;
        var emission = particleSystem.emission;
        this.emissionModule = emission;
    }
    void Update()
    {
        //var emission = particleSystem.emission;
        var emission = this.emissionModule;


        emission.rateOverTime = new ParticleSystem.MinMaxCurve(emissionRate);
    }
}

NullReferenceException: Do not create your own module instances, get them from a ParticleSystem instance
UnityEngine.ParticleSystem+EmissionModule.set_rateOverTime (UnityEngine.ParticleSystem+MinMaxCurve value) (at <893f889776d241068c95ad83f5452958>:0)
ParticleSystemController.Update ()