Fix nested optionals with empty values in the middle

implementation/src/main/java/io/smallrye/config/ConfigMappingProvider.java

@@ -323,9 +323,19 @@ private void processLazyPropertyInGroup(
 
         if (optional && property.asOptional().getNestedProperty().isGroup()) {
             GroupProperty nestedGroup = property.asOptional().getNestedProperty().asGroup();
+            // To recursively create Optional nested groups
+            BiFunction<ConfigMappingContext, NameIterator, ConfigMappingObject> delegate = new BiFunction<ConfigMappingContext, NameIterator, ConfigMappingObject>() {
+                @SuppressWarnings("unchecked")
+                @Override
+                public ConfigMappingObject apply(ConfigMappingContext configMappingContext, NameIterator nameIterator) {
+                    if (matchAction instanceof BiFunction) {
+                        return (ConfigMappingObject) ((BiFunction) matchAction).apply(configMappingContext, nameIterator);
+                    }
+                    return null;
+                }
+            };
             GetOrCreateEnclosingGroupInGroup nestedMatchAction = new GetOrCreateEnclosingGroupInGroup(
-                    property.isParentPropertyName() ? getEnclosingFunction
-                            : new ConsumeOneAndThenFn<>(getEnclosingFunction),
+                    property.isParentPropertyName() ? delegate : new ConsumeOneAndThenFn<>(delegate),
                     group, nestedGroup, currentPath);
             processLazyGroupInGroup(currentPath, matchActions, defaultValues, namingStrategy, nestedGroup.getGroupType(),
                     nestedMatchAction,
@@ -727,10 +737,10 @@ static class GetFieldOfEnclosing implements BiFunction<ConfigMappingContext, Nam
             this.memberName = memberName;
         }
 
-        public ConfigMappingObject apply(final ConfigMappingContext mc, final NameIterator ni) {
-            ConfigMappingObject outer = getEnclosingFunction.apply(mc, ni);
+        public ConfigMappingObject apply(final ConfigMappingContext context, final NameIterator ni) {
+            ConfigMappingObject outer = getEnclosingFunction.apply(context, ni);
             // eagerly populated groups will always exist
-            return (ConfigMappingObject) mc.getEnclosedField(type, memberName, outer);
+            return (ConfigMappingObject) context.getEnclosedField(type, memberName, outer);
         }
     }
 

implementation/src/test/java/io/smallrye/config/ConfigMappingInterfaceTest.java

@@ -1387,4 +1387,31 @@ void envPropertiesWithoutDottedProperties() {
         assertEquals("p@ssw0rd", mapping.client().get().keystore().password());
         //assertFalse(mapping.client().get().endpoints().isEmpty());
     }
+
+    @ConfigMapping(prefix = "optionals")
+    interface NestedOptionals {
+        Optional<First> first();
+
+        interface First {
+            Optional<Second> second();
+
+            interface Second {
+                String value();
+            }
+        }
+    }
+
+    @Test
+    void nestedOptionals() throws Exception {
+        SmallRyeConfig config = new SmallRyeConfigBuilder()
+                .withMapping(NestedOptionals.class)
+                .withSources(config("optionals.first.second.value", "value"))
+                .build();
+
+        NestedOptionals mapping = config.getConfigMapping(NestedOptionals.class);
+
+        assertTrue(mapping.first().isPresent());
+        assertTrue(mapping.first().get().second().isPresent());
+        assertEquals("value", mapping.first().get().second().get().value());
+    }
 }