Tolerate endpoints without a location when detecting the local DC

core/src/main/java/tech/ydb/core/impl/pool/PriorityPicker.java

@@ -67,8 +67,12 @@ static String getLocationFromConfig(String preferable, String selfLocation) {
 
     @VisibleForTesting
     static String detectLocalDC(List<EndpointRecord> endpoints, Ticker ticker) {
+        // Endpoints without a known location carry no information about datacenters. They must be
+        // filtered out because groupingBy rejects a null key - the endpoint the transport bootstraps
+        // with has no location until the first discovery completes.
         Map<String, List<EndpointRecord>> dcLocationToNodes = endpoints
                 .stream()
+                .filter(endpoint -> endpoint.getLocation() != null && !endpoint.getLocation().isEmpty())
                 .collect(Collectors.groupingBy(EndpointRecord::getLocation));
 
         if (dcLocationToNodes.size() < 2) {

core/src/test/java/tech/ydb/core/impl/pool/PriorityPickerTest.java

@@ -9,6 +9,7 @@
 
 import javax.net.ServerSocketFactory;
 
+import com.google.common.base.Ticker;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -56,6 +57,19 @@ public void detectLocalDCFallbackTest() {
         Assert.assertEquals(0, ignoreSelfLocation.getEndpointPriority("DC3"));
     }
 
+    @Test
+    public void detectLocalDCWithoutLocationsTest() {
+        // the endpoint a transport bootstraps with has no location until the first discovery completes
+        List<EndpointRecord> bootstrap = Collections.singletonList(new EndpointRecord("localhost", 2136));
+        PriorityPicker picker = PriorityPicker.from(BalancingSettings.detectLocalDs(), null, bootstrap);
+
+        Assert.assertEquals(0, picker.getEndpointPriority("DC1"));
+        Assert.assertEquals(0, picker.getEndpointPriority(null));
+
+        Assert.assertNull(PriorityPicker.detectLocalDC(bootstrap, Ticker.systemTicker()));
+        Assert.assertNull(PriorityPicker.detectLocalDC(Collections.emptyList(), Ticker.systemTicker()));
+    }
+
     @Test
     public void detectLocalDCTest() {
         TestTicker testTicker = new TestTicker(