code: protected boolean checkUnderflow(final int slot) {
  		if (childs[slot] == NULL_ID) {
  			return false;
  		}
  		if (slot == 0) {
  			return checkUnderflowWithRight(slot); // use nodeParent right sibling
  		} else {
  			if (getSlotLeft(slot) == slot) {
  				return checkUnderflowWithRight(slot); // use nodeParent right sibling
  			} else {
  				return checkUnderflowWithLeft(slot);  // use nodeParent left sibling
  			}
  		}
  	}
docs: Check if underflow occurred in child of slot
  
  @param slot the index of a child in nodeParent (this)