| FillBackwardT(IEnumerableT) | Returns a sequence with each null reference or value in the source replaced with the following non-null reference or value in that sequence. |
| FillBackwardT(IEnumerableT, FuncT, Boolean) | Returns a sequence with each missing element in the source replaced with the following non-missing element in that sequence. An additional parameter specifies a function used to determine if an element is considered missing or not. |
| FillBackwardT(IEnumerableT, FuncT, Boolean, FuncT, T, T) | Returns a sequence with each missing element in the source replaced with the following non-missing element in that sequence. Additional parameters specify two functions, one used to determine if an element is considered missing or not and another to provide the replacement for the missing element. |