fix: better handling if confirmed block not found on node

web3.js/src/connection.js

@@ -448,6 +448,8 @@ const GetMinimumBalanceForRentExemptionRpcResult = jsonRpcResult('number');
  * Expected JSON RPC response for the "getConfirmedBlock" message
  */
 export const GetConfirmedBlockRpcResult = jsonRpcResult(
+  struct.union([
+    'null',
     struct({
       blockhash: 'string',
       previousBlockhash: 'string',
@@ -488,6 +490,7 @@ export const GetConfirmedBlockRpcResult = jsonRpcResult(
         }),
       ]),
     }),
+  ]),
 );
 
 /**
@@ -1052,6 +1055,9 @@ export class Connection {
       throw new Error(result.error.message);
     }
     assert(typeof result.result !== 'undefined');
+    if (!result.result) {
+      throw new Error('Confirmed block '+slot+' not found');
+    }
     return {
       blockhash: new PublicKey(result.result.blockhash).toString(),
       previousBlockhash: new PublicKey(

web3.js/test/connection.test.js

@@ -646,6 +646,21 @@ test('get confirmed block', async () => {
     }
     x++;
   }
+
+  mockRpc.push([
+    url,
+    {
+      method: 'getConfirmedBlock',
+      params: [10000],
+    },
+    {
+      error: null,
+      result: null,
+    },
+  ]);
+  await expect(
+    connection.getConfirmedBlock(10000),
+  ).rejects.toThrow();
 });
 
 test('get recent blockhash', async () => {