Fixing ComposableIndexTemplateTests (#130052)

Author: masseyke

muted-tests.yml

@@ -563,9 +563,6 @@ tests:
   issue: https://github.com/elastic/elasticsearch/issues/130010
 - class: org.elasticsearch.xpack.esql.qa.mixed.MixedClusterEsqlSpecIT
   issue: https://github.com/elastic/elasticsearch/issues/128224
-- class: org.elasticsearch.cluster.metadata.ComposableIndexTemplateTests
-  method: testMergeEmptyMappingsIntoTemplateWithNonEmptySettings
-  issue: https://github.com/elastic/elasticsearch/issues/130050
 - class: org.elasticsearch.xpack.esql.qa.multi_node.GenerativeIT
   method: test
   issue: https://github.com/elastic/elasticsearch/issues/130067

server/src/test/java/org/elasticsearch/cluster/metadata/ComposableIndexTemplateTests.java

@@ -352,7 +352,12 @@ public void testMergeEmptyMappingsIntoTemplateWithNonEmptySettings() throws IOEx
         // Attempting to merge in null mappings ought to fail
         ComposableIndexTemplate indexTemplate = randomInstance();
         expectThrows(NullPointerException.class, () -> indexTemplate.mergeMappings(null));
-        assertThat(indexTemplate.mergeMappings(EMPTY_MAPPINGS), equalTo(indexTemplate));
+        ComposableIndexTemplate mergedTemplate = indexTemplate.mergeMappings(EMPTY_MAPPINGS);
+        if (indexTemplate.template() == null || indexTemplate.template().mappings() == null) {
+            assertThat(mergedTemplate.template().mappings(), equalTo(EMPTY_MAPPINGS));
+        } else {
+            assertThat(mergedTemplate, equalTo(indexTemplate));
+        }
         assertThat(indexTemplate.mergeSettings(Settings.EMPTY), equalTo(indexTemplate));
     }