Turbotable - Multisort with null values doesn't quite work correctly

[ischemicbg]

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Current behavior
When multisort is enabled, columns that are sorted with null values return in random order when sorting the column multiple times

Expected behavior
To sort like single sort mode does

I believe this bug is because you're missing an 'else' here: https://github.com/primefaces/primeng/blob/master/src/app/components/table/table.ts#L771

        if (value1 == null && value2 != null)
            result = -1;
        else if (value1 != null && value2 == null)
            result = 1;
        else if (value1 == null && value2 == null)
            result = 0;
        if (typeof value1 == 'string' || value1 instanceof String) {
            if (value1.localeCompare && (value1 != value2)) {
                return (multiSortMeta[index].order * value1.localeCompare(value2));
            }
        }
        else {
            result = (value1 < value2) ? -1 : 1;
        }

Should be

        if (value1 == null && value2 != null)
            result = -1;
        else if (value1 != null && value2 == null)
            result = 1;
        else if (value1 == null && value2 == null)
            result = 0;
        else if (typeof value1 == 'string' || value1 instanceof String) {
            if (value1.localeCompare && (value1 != value2)) {
                return (multiSortMeta[index].order * value1.localeCompare(value2));
            }
        }
        else {
            result = (value1 < value2) ? -1 : 1;
        }

Like in singlesort. Otherwise the null checking is pretty much ignored.