remove custom error and adjust error message

src/errors.ts

@@ -325,12 +325,3 @@ export class ErrGasLimitShouldBe0ForInnerTransaction extends Err {
     super("gas limit must be 0 for the inner transaction for relayed v2");
   }
 }
-
-/**
- * Signals an optional class member is undefined
- */
-export class ErrOptionalClassMemberIsUndefined extends Err {
-  public constructor(message: string) {
-    super(message);
-  }
-}

src/transactionWatcher.ts

@@ -1,5 +1,5 @@
 import { AsyncTimer } from "./asyncTimer";
-import { Err, ErrExpectedTransactionEventsNotFound, ErrExpectedTransactionStatusNotReached, ErrOptionalClassMemberIsUndefined } from "./errors";
+import { Err, ErrExpectedTransactionEventsNotFound, ErrExpectedTransactionStatusNotReached } from "./errors";
 import { ITransactionFetcher } from "./interface";
 import { ITransactionEvent, ITransactionOnNetwork, ITransactionStatus } from "./interfaceOfNetwork";
 import { Logger } from "./logger";
@@ -71,7 +71,7 @@ export class TransactionWatcher {
     public async awaitCompleted(transaction: ITransaction): Promise<ITransactionOnNetwork> {
         const isCompleted = (transactionOnNetwork: ITransactionOnNetwork) => {
             if (transactionOnNetwork.isCompleted === undefined) {
-                throw new ErrOptionalClassMemberIsUndefined("`isCompleted` is undefined. getTransaction() should be called using `withProcessStatus=true`.");
+                throw new Err("The transaction watcher requires the isCompleted property to be defined on the transaction object. Perhaps you've used the sdk-network-provider's getTransaction() and in that case you should also pass `withProcessStatus=true`.");
             }
             return transactionOnNetwork.isCompleted
         };