short circuit empty Map if no index (#49)

* short circuit empty Map if no index

* add test to check single index create and release with release rotation

* rename for more clarity

* fix comment

Author: jaserud

src/main/java/bio/overture/rollcall/repository/IndexRepository.java

@@ -140,7 +140,11 @@ public boolean deleteIndices(@NonNull String... indices) {
   }
 
   @SneakyThrows
-  public Map<String, Date> getIndicesMappedToCreationDate(String... indices) {
+  public Map<String, Date> getIndicesMappedToCreationDate(@NonNull String... indices) {
+    if (indices.length == 0) {
+      return Map.of();
+    }
+
     val response = client.indices().get(new GetIndexRequest(indices).indicesOptions(IndicesOptions.lenientExpand()), RequestOptions.DEFAULT);
 
     val indicesSettings = response.getSettings();

src/test/java/bio/overture/rollcall/service/AliasServiceTest.java

@@ -126,6 +126,21 @@ public void testReleaseNonDestructiveFailurePreFlight() {
     assertThat(state2.get(INDEX2).get(0).alias()).isEqualTo("file_centric");
   }
 
+  @Test
+  @SneakyThrows
+  public void testReleaseNewIndexWithRotationOn() {
+    val NEW_INDEX = "file_centric_sd_asdfca_re_1";
+    client.indices().create(new CreateIndexRequest(NEW_INDEX), RequestOptions.DEFAULT);
+
+    // release re_1 for index shard sd_asdfca
+    val request1 = new AliasRequest("file_centric", "re_1", Lists.list( "sd_asdfca"));
+    service.release(request1);
+
+    // verify aliases assigned to indices
+    val state1 = repository.getAliasState();
+    assertThat(state1.get(NEW_INDEX).get(0).alias()).isEqualTo("file_centric");
+  }
+
   @Test
   @SneakyThrows
   public void testReleaseAndDeleteOldIndices() {