fix 'node show' and 'shard explain' crashes (#86)

pkg/es/shard.go

@@ -163,30 +163,37 @@ func ShardAllocation(conf *cfg.Config, index string) error {
 
 	slog.Debug("ES result", "explain", res)
 
-	currentNode := res.CurrentNode
-
 	table := printer.NewTable(conf, 2, 10)
 	table.Addheaders("shard allocation setting", "value")
 
-	roles := make([]string, len(currentNode.Roles))
-	for idx, role := range currentNode.Roles {
-		roles[idx] = role.Name
-	}
-
 	table.Entries = [][]any{
 		{"Index", index},
 		{"Current state", res.CurrentState},
-		{"Current node", currentNode.Name},
-		{"Current k8s node", currentNode.Attributes["k8s_node_name"]},
-		{"Current node address", currentNode.TransportAddress},
-		{"Current node id", currentNode.Id},
-		{"Current node weight", currentNode.WeightRanking},
-		{"Current node roles", roles},
 		{"Can rebalance cluster", res.CanRebalanceCluster.Name},
 		{"Can rebalance to another node", res.CanRebalanceToOtherNode.Name},
 		{"Can remain on current node", res.CanRemainOnCurrentNode.Name},
 	}
 
+	if res.CurrentNode != nil {
+		currentNode := res.CurrentNode
+		roles := make([]string, len(currentNode.Roles))
+
+		for idx, role := range currentNode.Roles {
+			roles[idx] = role.Name
+		}
+
+		table.Entries = append(table.Entries, [][]any{
+			{"Current node", currentNode.Name},
+			{"Current k8s node", currentNode.Attributes["k8s_node_name"]},
+			{"Current node address", currentNode.TransportAddress},
+			{"Current node id", currentNode.Id},
+			{"Current node weight", currentNode.WeightRanking},
+			{"Current node roles", roles},
+		}...)
+	} else {
+		table.AddRow("Current node", "not currently assigned to any node")
+	}
+
 	if res.CurrentState == "unassigned" {
 		table.AddRow("Unassignment reason", res.UnassignedInfo.Reason.String()+" at "+res.UnassignedInfo.At.(string))
 	}