Marek Kasik authored Mar 27, 2020 and Uli Schlachter committed Nov 20, 2020

Operators BlueValues, OtherBlues, FamilyBlues, FamilyOtherBlues,
StemSnapH and StemSnapV have operands of type delta which can be
a number or an array of delta-encoded numbers. This array can be
empty according to freetype developers.
This commit checks whether current operator is among those listed
and permits empty operand in such case.