Guard pool login before first block template

lib/pool.js

@@ -418,6 +418,9 @@ Miner.prototype = {
 	},
 	getJob: function () {
 		let blockTemplate = currentBlockTemplate[0];
+		if (!blockTemplate) {
+			return null;
+		}
 		let newJob = {
 			id: utils.uid(),
 			height: blockTemplate.height,
@@ -625,10 +628,16 @@ function handleMinerMethod (method, params, ip, portData, sendReply, pushMessage
 			let minerId = utils.uid();
 			miner = new Miner(rewardType, minerId, login, pass, ip, port, params.agent, difficulty, noRetarget, pushMessage);
 			connectedMiners[minerId] = miner;
+			let minerJob = miner.getJob();
+			if (!minerJob) {
+				delete connectedMiners[minerId];
+				sendReply('No active block template yet');
+				return;
+			}
 
 			sendReply(null, {
 				id: minerId,
-				job: miner.getJob(),
+				job: minerJob,
 				status: 'OK'
 			});
 
@@ -640,7 +649,12 @@ function handleMinerMethod (method, params, ip, portData, sendReply, pushMessage
 				return;
 			}
 			miner.heartbeat();
-			sendReply(null, miner.getJob());
+			let jobReply = miner.getJob();
+			if (!jobReply) {
+				sendReply('No active block template yet');
+				return;
+			}
+			sendReply(null, jobReply);
 			break;
 		case 'submit':
 			if (!miner) {