abhishekagarwal87 commented on a change in pull request #10869:
URL: https://github.com/apache/druid/pull/10869#discussion_r573525491



##########
File path: 
core/src/main/java/org/apache/druid/guice/GuiceAnnotationIntrospector.java
##########
@@ -101,13 +103,28 @@ public Object findInjectableValueId(AnnotatedMember m)
     // delegate creators. I'm not 100% sure why it's not called, but guess 
it's because the argument
     // is some Java type that Jackson already knows how to deserialize. Since 
there is only one argument,
     // Jackson perhaps is able to just deserialize it without introspection.
+
     if (ac instanceof AnnotatedParameter) {
       final AnnotatedParameter ap = (AnnotatedParameter) ac;
       if (ap.hasAnnotation(JsonProperty.class)) {
         return JsonIgnoreProperties.Value.empty();
       }
     }
 
-    return JsonIgnoreProperties.Value.forIgnoredProperties("");
+    // A map can have empty string keys e.g. 
https://github.com/apache/druid/issues/10859. By returning empty ignored
+    // list for map, we can allow for empty string keys in a map. A nested 
class within map
+    // can still be annotated with JacksonInject and still be 
non-deserializable from user input
+    // Refer to {@link 
com.fasterxml.jackson.databind.deser.BasicDeserializerFactory.createMapDeserializer}
 for details
+    // on how the ignored list is passed to map deserializer
+    if (ac instanceof AnnotatedClass) {
+      final AnnotatedClass aClass = (AnnotatedClass) ac;
+      if (Map.class.isAssignableFrom(aClass.getAnnotated())) {
+        return JsonIgnoreProperties.Value.empty();
+      }
+    }
+
+    // We will allow serialization on empty properties. Properties marked with 
{@code @JacksonInject} are still
+    // not serialized if there is no getter marked with {@code @JsonProperty}
+    return 
JsonIgnoreProperties.Value.forIgnoredProperties("").withAllowGetters();

Review comment:
       `JsonIgnoreProperties.Value` has following fields
   ```
           protected final Set<String> _ignored;
           protected final boolean _ignoreUnknown;
           protected final boolean _allowGetters;
           protected final boolean _allowSetters;
           protected final boolean _merge
   ```
   `_allowGetters` controls whether we will populate the field during 
serialization. By default, `_allowGetters` is set to false if using 
`forIgnoredProperties` but we override it to `true` using `withAllowGetters`




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