Replace all the nulls in a list.

Input parameters:

1. Li → List with nulls to replace.
2. Rp → Optional replacement value.
3. Mt → Replacement method.
   • 0 → None
   • 1 → Value
   • 2 → Closest (L)
   • 3 → Closest (T)
   • 4 → Leading
   • 5 → Leading*
   • 6 → Trailing
   • 7 → Trailing*

Output parameters:

1. Li → List with replaced nulls.
2. Rn → Number of replacements.