feat: for nullable primitives return a default value (#1284)

* feat: return default values for non-null fields, since primitives cannot be null in assembly script

* update examples

* ci

Author: saihaj

.changeset/fifty-eyes-obey.md

@@ -0,0 +1,5 @@
+---
+'@graphprotocol/graph-cli': minor
+---
+
+Changing code generation so we reduce the non-null assertions for primitive types. This way we can return null for primitive types and still have the generated code compile. 

examples/basic-event-handlers/generated/schema.ts

@@ -35,7 +35,11 @@ export class NewGravatar extends Entity {
 
   get id(): string {
     let value = this.get("id");
-    return value!.toString();
+    if (!value || value.kind == ValueKind.NULL) {
+      throw new Error("Cannot return null for a required field.");
+    } else {
+      return value.toString();
+    }
   }
 
   set id(value: string) {
@@ -44,7 +48,11 @@ export class NewGravatar extends Entity {
 
   get owner(): Bytes {
     let value = this.get("owner");
-    return value!.toBytes();
+    if (!value || value.kind == ValueKind.NULL) {
+      throw new Error("Cannot return null for a required field.");
+    } else {
+      return value.toBytes();
+    }
   }
 
   set owner(value: Bytes) {
@@ -53,7 +61,11 @@ export class NewGravatar extends Entity {
 
   get displayName(): string {
     let value = this.get("displayName");
-    return value!.toString();
+    if (!value || value.kind == ValueKind.NULL) {
+      throw new Error("Cannot return null for a required field.");
+    } else {
+      return value.toString();
+    }
   }
 
   set displayName(value: string) {
@@ -62,7 +74,11 @@ export class NewGravatar extends Entity {
 
   get imageUrl(): string {
     let value = this.get("imageUrl");
-    return value!.toString();
+    if (!value || value.kind == ValueKind.NULL) {
+      throw new Error("Cannot return null for a required field.");
+    } else {
+      return value.toString();
+    }
   }
 
   set imageUrl(value: string) {
@@ -94,7 +110,11 @@ export class UpdatedGravatar extends Entity {
 
   get id(): string {
     let value = this.get("id");
-    return value!.toString();
+    if (!value || value.kind == ValueKind.NULL) {
+      throw new Error("Cannot return null for a required field.");
+    } else {
+      return value.toString();
+    }
   }
 
   set id(value: string) {
@@ -103,7 +123,11 @@ export class UpdatedGravatar extends Entity {
 
   get owner(): Bytes {
     let value = this.get("owner");
-    return value!.toBytes();
+    if (!value || value.kind == ValueKind.NULL) {
+      throw new Error("Cannot return null for a required field.");
+    } else {
+      return value.toBytes();
+    }
   }
 
   set owner(value: Bytes) {
@@ -112,7 +136,11 @@ export class UpdatedGravatar extends Entity {
 
   get displayName(): string {
     let value = this.get("displayName");
-    return value!.toString();
+    if (!value || value.kind == ValueKind.NULL) {
+      throw new Error("Cannot return null for a required field.");
+    } else {
+      return value.toString();
+    }
   }
 
   set displayName(value: string) {
@@ -121,7 +149,11 @@ export class UpdatedGravatar extends Entity {
 
   get imageUrl(): string {
     let value = this.get("imageUrl");
-    return value!.toString();
+    if (!value || value.kind == ValueKind.NULL) {
+      throw new Error("Cannot return null for a required field.");
+    } else {
+      return value.toString();
+    }
   }
 
   set imageUrl(value: string) {