[Fix] CompletionMapper throws misleading error on null value

closes #6399

src/main/java/org/elasticsearch/index/mapper/FieldMapper.java

@@ -286,6 +286,8 @@ public interface FieldMapper<T> extends Mapper {
 
     boolean isSortable();
 
+    boolean supportsNullValue();
+
     boolean hasDocValues();
 
     Loading normsLoading(Loading defaultLoading);

src/main/java/org/elasticsearch/index/mapper/core/AbstractFieldMapper.java

@@ -842,6 +842,11 @@ public abstract class AbstractFieldMapper<T> implements FieldMapper<T> {
         return true;
     }
 
+    @Override
+    public boolean supportsNullValue() {
+        return true;
+    }
+
     public boolean hasDocValues() {
         return docValues;
     }

src/main/java/org/elasticsearch/index/mapper/core/CompletionFieldMapper.java

@@ -451,6 +451,11 @@ public class CompletionFieldMapper extends AbstractFieldMapper<String> {
         return false;
     }
 
+    @Override
+    public boolean supportsNullValue() {
+        return false;
+    }
+
     @Override
     public FieldType defaultFieldType() {
         return Defaults.FIELD_TYPE;

src/main/java/org/elasticsearch/index/mapper/object/ObjectMapper.java

@@ -532,6 +532,11 @@ public class ObjectMapper implements Mapper, AllFieldMapper.IncludeInAll {
         // we can only handle null values if we have mappings for them
         Mapper mapper = mappers.get(lastFieldName);
         if (mapper != null) {
+            if (mapper instanceof FieldMapper) {
+                if (!((FieldMapper) mapper).supportsNullValue()) {
+                    throw new MapperParsingException("no object mapping found for null value in [" + lastFieldName + "]");
+                }
+            }
             mapper.parse(context);
         }
     }

src/test/java/org/elasticsearch/search/suggest/CompletionSuggestSearchTests.java

@@ -1039,6 +1039,38 @@ public class CompletionSuggestSearchTests extends ElasticsearchIntegrationTest {
         }
     }
 
+    // see issue #6399
+    @Test
+    public void testIndexingUnrelatedNullValue() throws Exception {
+        String mapping = jsonBuilder()
+                .startObject()
+                .startObject(TYPE)
+                .startObject("properties")
+                .startObject(FIELD)
+                .field("type", "completion")
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .string();
+
+        assertAcked(client().admin().indices().prepareCreate(INDEX).addMapping(TYPE, mapping).get());
+        ensureGreen();
+
+        client().prepareIndex(INDEX, TYPE, "1").setSource(FIELD, "strings make me happy", FIELD + "_1", "nulls make me sad")
+        .setRefresh(true).get();
+
+        try {
+            client().prepareIndex(INDEX, TYPE, "2").setSource(FIELD, null, FIELD + "_1", "nulls make me sad")
+                    .setRefresh(true).get();
+            fail("Expected MapperParsingException for null value");
+        } catch (MapperParsingException e) {
+            // make sure that the exception has the name of the field causing the error
+            assertTrue(e.getDetailedMessage().contains(FIELD));
+        }
+
+    }
+
     private static String replaceReservedChars(String input, char replacement) {
         char[] charArray = input.toCharArray();
         for (int i = 0; i < charArray.length; i++) {