多年平均计算（不包括NULL）

Question

我想计算过去5年中公司的平均得分。在计算中不包括NULL（但包括0）。以下是数据：

Company    Year Score
Company A   2014    1
Company B   2014    1
Company C   2014    
Company D   2014    0
Company A   2015    1
Company B   2015    0
Company C   2015    
Company D   2015    0
Company A   2016    1
Company B   2016    1
Company C   2016    1
Company D   2016    1
Company A   2017    1
Company B   2017    1
Company C   2017    1
Company D   2017    1
Company A   2018    1
Company B   2018    1
Company C   2018    1
Company D   2018    1

基本上，如果您看到C公司和D公司看起来相似。但是，2014年和2015年，公司C的得分为NULL，而公司D的得分为0。

C的平均值为100％（3/3），而D公司的平均值为60％（3/5）

使用以下代码，对于没有NULL的公司，我可以完美地实现结果：

_COL_Liquidity Score 2 = 
    VAR MaxSelectedYear = 'Data'[Year]
    VAR OnePriorYear = MaxSelectedYear - 1
    VAR TwoPriorYear = MaxSelectedYear - 2
    VAR ThreePriorYear = MaxSelectedYear - 3
    VAR FourPriorYear = MaxSelectedYear - 4
    VAR MinYearInData = MINX(ALL('Data'), 'Raw Data'[Year])
    RETURN
        DIVIDE(
            CALCULATE(SUM('Data'[Score]), FILTER(ALLEXCEPT('Data',Company), 'Raw Data'[Year] = MaxSelectedYear))
            +
            CALCULATE(SUM('Data'[Score]), FILTER(ALLEXCEPT('Data',Company), 'Raw Data'[Year] = OnePriorYear))
            +
            CALCULATE(SUM('Data'[Score]), FILTER(ALLEXCEPT('Data',Company), 'Raw Data'[Year] = TwoPriorYear))
            +
            CALCULATE(SUM('Data'[Score]), FILTER(ALLEXCEPT('Data',Company), 'Raw Data'[Year] = ThreePriorYear))
            +
            CALCULATE(SUM('Data'[Score]), FILTER(ALLEXCEPT('Data',Company), 'Raw Data'[Year] = FourPriorYear))
            ,
            IF(OnePriorYear < MinYearInData, 1, 
                IF(TwoPriorYear < MinYearInData,2,
                    IF(ThreePriorYear < MinYearInData, 3,
                        IF(FourPriorYear < MinYearInData, 4,5)
                    )
                )
            ),
            BLANK()
        )

预期输出：

Company A - 100%
Company B - 80%
Company C - 100%
Company D - 60%