diff --git a/src/Story.ts b/src/Story.ts
index 7fc0dc7a..8bda8243 100644
--- a/src/Story.ts
+++ b/src/Story.ts
@@ -1202,7 +1202,7 @@ export class Story extends InkObject{
 			throw new Error("Can't " + activityStr + '. Story is in the middle of a ContinueAsync(). Make more ContinueAsync() calls or a single Continue() call beforehand.');
 	}
 
-	public ChoosePath(p: Path | null){
+	public ChoosePath(p: Path){
 		this.state.SetChosenPath(p);
 
 		// Take a note of newly visited containers for read counts etc
@@ -1216,6 +1216,7 @@ export class Story extends InkObject{
 
 		let choiceToChoose = choices[choiceIdx];
 		if (choiceToChoose.threadAtGeneration === null) { return throwNullException('choiceToChoose.threadAtGeneration'); }
+		if (choiceToChoose.targetPath === null) { return throwNullException('choiceToChoose.targetPath'); }
 
 		this.state.callStack.currentThread = choiceToChoose.threadAtGeneration;
 
@@ -1656,6 +1657,8 @@ export class Story extends InkObject{
 
 		let choice = invisibleChoices[0];
 
+		if (choice.targetPath === null) { return throwNullException('choice.targetPath'); }
+
 		this.ChoosePath(choice.targetPath);
 
 		return true;
diff --git a/src/StoryState.ts b/src/StoryState.ts
index 61b33635..f8eae31c 100644
--- a/src/StoryState.ts
+++ b/src/StoryState.ts
@@ -12,7 +12,7 @@ import {JsonSerialisation} from './JsonSerialisation';
 import {PRNG} from './PRNG';
 import {Void} from './Void';
 import {Pointer} from './Pointer';
-import { tryGetValueFromMap } from './TryGetResult';
+import {tryGetValueFromMap} from './TryGetResult';
 import {Choice} from './Choice';
 import {asOrNull, asOrThrows, nullIfUndefined} from './TypeAssertion';
 import {JObject} from './JObject';
@@ -20,6 +20,7 @@ import {Debug} from './Debug';
 import {Container} from './Container';
 import {InkObject} from './Object';
 import { throwNullException } from './NullException';
+import { Story } from './Story';
 
 export class StoryState{
 
@@ -108,7 +109,7 @@ export class StoryState{
 	public previousRandom: number = 0;
 	public didSafeExit: boolean = false;
 
-	public story: any /* Story */;
+	public story: Story;
 
 	get currentPathString(){
 		let pointer = this.currentPointer;
@@ -221,7 +222,7 @@ export class StoryState{
 		this.callStack.currentElement.inExpressionEvaluation = value;
 	}
 
-	constructor(story: any /* Story */){
+	constructor(story: Story){
 		this.story = story;
 
 		this._outputStream = [];
@@ -672,7 +673,9 @@ export class StoryState{
 				rawList.origins.length = 0;
 
 				for (let n of rawList.originNames) {
+					if (this.story.listDefinitions === null) return throwNullException('StoryState.story.listDefinitions');
 					let def = this.story.listDefinitions.TryListGetDefinition(n, null);
+					if (def.result === null) return throwNullException('StoryState def.result');
 					if (rawList.origins.indexOf(def.result) < 0) rawList.origins.push(def.result);
 				}
 			}
@@ -749,7 +752,7 @@ export class StoryState{
 		this.callStack.Pop(popType);
 	}
 
-	public SetChosenPath(path: Path | null){
+	public SetChosenPath(path: Path){
 		// Changing direction, assume we need to clear current set of choices
 		this._currentChoices.length = 0;
 
diff --git a/src/VariablesState.ts b/src/VariablesState.ts
index e2405cb1..f0336bef 100644
--- a/src/VariablesState.ts
+++ b/src/VariablesState.ts
@@ -86,7 +86,7 @@ export class VariablesState{
 		}
 	}
 
-	constructor(callStack: CallStack, listDefsOrigin: ListDefinitionsOrigin){
+	constructor(callStack: CallStack, listDefsOrigin: ListDefinitionsOrigin | null){
 		this._globalVariables = new Map();
 		this._callStack = callStack;
 		this._listDefsOrigin = listDefsOrigin;
@@ -173,6 +173,7 @@ export class VariablesState{
 			if (variableValue.exists)
 				return variableValue.result;
 
+			if (this._listDefsOrigin === null) return throwNullException('VariablesState._listDefsOrigin');
 			let listItemValue = this._listDefsOrigin.FindSingleItemListWithName(name);
 			if (listItemValue)
 				return listItemValue;
@@ -306,5 +307,5 @@ export class VariablesState{
 
 	private _callStack: CallStack;
 	private _changedVariables: Set<string> | null = new Set();
-	private _listDefsOrigin: ListDefinitionsOrigin;
+	private _listDefsOrigin: ListDefinitionsOrigin | null;
 }