Update migration-guide-5.2-5.3.adoc

Author: sothawo

src/main/antora/modules/ROOT/pages/migration-guides/migration-guide-5.2-5.3.adoc

@@ -5,7 +5,10 @@ This section describes breaking changes from version 5.2.x to 5.3.x and how remo
 
 [[elasticsearch-migration-guide-5.2-5.3.breaking-changes]]
 == Breaking Changes
-
+During the parameter replacement in `@Query` annotated repository methods previous versions wrote the String _"null"_ into the query that was sent to Elasticsearch 
+when the actual parameter value was `null`. As Elasticsearch does not store `null` values, this behaviour could lead to problems, for example whent the fields to be 
+searched contains the string `"null"`. In Version 5.3 a `null` value in a parameter will cause a `ConversionException` to be thrown. If you are using `"null"` as the 
+`null_value` defined in a field mapping, then pass that string into the query instead of a Java `null`.
 
 [[elasticsearch-migration-guide-5.2-5.3.deprecations]]
 == Deprecations