[7.x] Fix NPE when building exception messages for aggregations (#59156)

server/src/main/java/org/elasticsearch/search/aggregations/support/ValuesSourceRegistry.java

@@ -18,7 +18,6 @@
  */
 package org.elasticsearch.search.aggregations.support;
 
-import org.elasticsearch.index.mapper.MappedFieldType;
 import org.elasticsearch.index.query.QueryShardContext;
 import org.elasticsearch.search.SearchModule;
 import org.elasticsearch.search.aggregations.AggregationExecutionException;
@@ -123,11 +122,10 @@ public AggregatorSupplier getAggregator(ValuesSourceConfig valuesSourceConfig, S
                 aggregatorRegistry.get(aggregationName)
             );
             if (supplier == null) {
-                // TODO: push building the description into ValuesSourceConfig
-                MappedFieldType fieldType = valuesSourceConfig.fieldContext().fieldType();
-                String fieldDescription = fieldType.typeName();
-                throw new IllegalArgumentException("Field [" + fieldType.name() + "] of type [" + fieldDescription +
-                    "] is not supported for aggregation [" + aggregationName + "]");            }
+                throw new IllegalArgumentException(
+                    valuesSourceConfig.getDescription() + " is not supported for aggregation [" + aggregationName + "]"
+                );
+            }
             return supplier;
         }
         throw  new AggregationExecutionException("Unregistered Aggregation [" + aggregationName + "]");

server/src/test/java/org/elasticsearch/search/aggregations/support/ValuesSourceRegistryTests.java

@@ -0,0 +1,68 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.search.aggregations.support;
+
+import org.elasticsearch.index.query.QueryShardContext;
+import org.elasticsearch.script.AggregationScript;
+import org.elasticsearch.test.ESTestCase;
+import org.mockito.Mockito;
+
+import java.util.Collections;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class ValuesSourceRegistryTests extends ESTestCase {
+
+    public void testAggregatorNotFoundException() {
+        final QueryShardContext queryShardContext = mock(QueryShardContext.class);
+        final AggregationScript.Factory mockAggScriptFactory = mock(AggregationScript.Factory.class);
+        when(mockAggScriptFactory.newFactory(Mockito.any(), Mockito.any())).thenReturn(mock(AggregationScript.LeafFactory.class));
+        when(queryShardContext.compile(Mockito.any(), Mockito.any())).thenReturn(mockAggScriptFactory);
+
+        ValuesSourceConfig fieldOnly = ValuesSourceConfig.resolve(
+            queryShardContext,
+            null,
+            "field",
+            null,
+            null,
+            null,
+            null,
+            CoreValuesSourceType.BYTES
+        );
+
+        ValuesSourceConfig scriptOnly = ValuesSourceConfig.resolve(
+            queryShardContext,
+            null,
+            null,
+            mockScript("fakeScript"),
+            null,
+            null,
+            null,
+            CoreValuesSourceType.BYTES
+        );
+        ValuesSourceRegistry registry = new ValuesSourceRegistry(
+            Collections.singletonMap("bogus", Collections.emptyList()),
+            null);
+        expectThrows(IllegalArgumentException.class, () -> registry.getAggregator(fieldOnly, "bogus"));
+        expectThrows(IllegalArgumentException.class, () -> registry.getAggregator(scriptOnly, "bogus"));
+    }
+
+}