core: handle empty proxy selector result

Author: mfperminov

core/src/main/java/io/grpc/internal/ProxyDetectorImpl.java

@@ -207,6 +207,10 @@ private ProxiedSocketAddress detectProxy(InetSocketAddress targetAddr) throws IO
     }
 
     List<Proxy> proxies = proxySelector.select(uri);
+    if (proxies == null || proxies.isEmpty()) {
+      log.log(Level.FINE, "No proxies returned, proceeding without proxy");
+      return null;
+    }
     if (proxies.size() > 1) {
       log.warning("More than 1 proxy detected, gRPC will select the first one");
     }

core/src/test/java/io/grpc/internal/ProxyDetectorImplTest.java

@@ -40,6 +40,7 @@
 import java.net.ProxySelector;
 import java.net.SocketAddress;
 import java.net.URI;
+import java.util.Collections;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -191,4 +192,11 @@ public ProxySelector get() {
         authenticator);
     assertNull(proxyDetector.proxyFor(destination));
   }
+
+  @Test
+  public void returnNullWhenProxySelectorReturnsEmptyList() throws Exception {
+    when(proxySelector.select(any(URI.class))).thenReturn(Collections.<Proxy>emptyList());
+
+    assertNull(proxyDetector.proxyFor(destination));
+  }
 }