For fastline series support for null points has been redesigned. Now the series handles null points in three different ways:
1) Do not paint null points : null points are not painted (gaps in line)
2) Skip null points : null points are not painted, but the regular points are connected with line (no gaps)
3) Ignore null points: null points are ignored.

NOTE: The IgnoreNulls property has been deprecated. Use the TreatNullsStyle.IGNORE and TreatNullsStyle.DONOTPAINT to mimic the behaviour of IgnoreNulls.