Reduce/Solve

RandomReal/RandomInteger

First argument of them can be a distribution. See:

RandomReal in combination with NormalDistribution

Reduce/Solve

Function

Null can be used as 1st argument of Function, for example

Function[, Sin[#]]

is equivalent to

Function[Sin[#]]

It's usually only used when you want to use the 3-arg form with SlotSequence. For example

Function[Null, Hold[Plus[##]], HoldAll]

ListPlot/ListLinePlot

ListPlot/ListLinePlot

Function[Null, ...] is an undocumented way to define a function that uses Slot arguments, for example

Null can be used as 1st argument of Function, for example