HSEARCH-2434 When validating Elasticsearch schemas, use "default" as …

…a default value for analyzer references

Because this is what Elasticsearch implies when it doesn't display the
analyzer attribute in retrieved mappings. It used not to matter on ES2,
because ES always displayed the analyzer attribute, but on ES5 it is no
longer the case.

elasticsearch/src/main/java/org/hibernate/search/elasticsearch/schema/impl/Elasticsearch2SchemaValidator.java

@@ -616,7 +616,7 @@ public void validate(ValidationErrorCollector errorCollector, PropertyMapping ex
 			validateJsonPrimitive( errorCollector, expectedMapping.getType(), "null_value",
 					expectedMapping.getNullValue(), actualMapping.getNullValue() );
 
-			validateEqualWithDefault( errorCollector, "analyzer", expectedMapping.getAnalyzer(), actualMapping.getAnalyzer(), null );
+			validateEqualWithDefault( errorCollector, "analyzer", expectedMapping.getAnalyzer(), actualMapping.getAnalyzer(), "default" );
 
 			super.validate( errorCollector, expectedMapping, actualMapping );