@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((direction == null) ? 0 : direction.hashCode());
		result = prime * result + row;
		return result;
	}
Returns the child level of this level.  The child of a level has the same direction 
as this level, with a distance of one more than this level.

@param the direction of the child
@return returns the child level of this level
@throws IllegalArgumentException if this is the source level, which is row 1
Ghidra/Features/GraphFunctionCalls/src/main/java/functioncalls/graph/FcgLevel.java