How do I make default values?

public bool isPossible;
public List needsList;
public List itemsList;
public Connection(bool newIsPossible, List newItemList, List newNeedsList) {
isPossible = newIsPossible;
itemsList = newItemList;
needsList = newNeedsList;
}

I want newNeedsList to be null as default.

A quick search… Default Parameter Specifiers Are Not Permitted - Unity Answers

Also, if that doesn’t work you can always do what’s done in languages without default parameters: function (or constructor) overload.

    public bool isPossible;
    public List<string> needsList;
    public List<string> itemsList;

    public Connection(bool newIsPossible, List<string> newItemList, List<string> newNeedsList) {
        isPossible = newIsPossible;
        itemsList = newItemList;
        needsList = newNeedsList;
    }

    public Connection(bool newIsPossible, List<string> newItemList) :
           this(newIsPossible,newItemList,null) {
    }

An then:

Connection(something, somethingElse); //will automatically match the second Connection constructor
Connection(something, somethingElse, moreStuff); //will automatically match the first one