RepeatedNull

p... or RepeatedNull[p] is a pattern object that represents a sequence of zero or more expressions, each matching p. 

RepeatedNull[p,max] represents from 0 to max expressions matching p.

RepeatedNull[p,{min,max}] represents between min and max expressions matching p.

RepeatedNull[p,{n}] represents exactly n expressions matching p.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.