Fix issue with null value in JSON. (#2728)

* Fix issue with null value in JSON.

Resolves #2720

* Fix copyright errors

* fix compiler errors

* fix null value in arrays

config/hocon/src/main/java/io/helidon/config/hocon/HoconConfigParserBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2018 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2021 Oracle and/or its affiliates. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -92,6 +92,7 @@ public HoconConfigParserBuilder resolveOptions(ConfigResolveOptions resolveOptio
      *
      * @return new instance of HOCON ConfigParser.
      */
+    @Override
     public ConfigParser build() {
         return new HoconConfigParser(resolvingEnabled, resolveOptions);
     }

config/hocon/src/main/java/io/helidon/config/hocon/internal/HoconConfigParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2018 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2021 Oracle and/or its affiliates. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -131,7 +131,12 @@ private static ObjectNode fromConfig(ConfigObject config) {
                     } else if (value instanceof ConfigObject) {
                         builder.addObject(key, fromConfig((ConfigObject) value));
                     } else {
-                        builder.addValue(key, value.unwrapped().toString());
+                        Object unwrapped = value.unwrapped();
+                        if (unwrapped == null) {
+                            builder.addValue(key, "");
+                        } else {
+                            builder.addValue(key, String.valueOf(unwrapped));
+                        }
                     }
                 });
         return builder.build();
@@ -145,7 +150,12 @@ private static ListNode fromList(ConfigList list) {
             } else if (value instanceof ConfigObject) {
                 builder.addObject(fromConfig((ConfigObject) value));
             } else {
-                builder.addValue(value.unwrapped().toString());
+                Object unwrapped = value.unwrapped();
+                if (unwrapped == null) {
+                    builder.addValue("");
+                } else {
+                    builder.addValue(String.valueOf(unwrapped));
+                }
             }
         });
         return builder.build();

config/hocon/src/test/java/io/helidon/config/hocon/HoconConfigParserTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2018 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2021 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.Set;
 import java.util.function.Function;
 import java.util.stream.Collectors;
@@ -47,6 +48,7 @@
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.hamcrest.Matchers.empty;
+import static org.hamcrest.Matchers.hasItems;
 import static org.hamcrest.Matchers.hasSize;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.is;
@@ -276,6 +278,26 @@ public void testCustomTypeMapping() {
 
     }
 
+    @Test
+    void testParserFromJson() {
+        Config config = Config.builder()
+                .disableSystemPropertiesSource()
+                .disableEnvironmentVariablesSource()
+                .disableParserServices()
+                .addParser(new HoconConfigParser())
+                .sources(ConfigSources.classpath("config.json"))
+                .build();
+
+        Optional<String> property = config.get("oracle.com").asString().asOptional();
+        assertThat(property, is(Optional.of("1")));
+
+        property = config.get("nulls.null").asString().asOptional();
+        assertThat(property, is(Optional.of("")));
+
+        List<String> properties = config.get("nulls-array").asList(String.class).get();
+        assertThat(properties, hasItems("test", ""));
+    }
+
     //
     // helper
     //
@@ -311,11 +333,11 @@ public static class AppType {
                 + "  storagePassphrase = \"${AES=thisIsEncriptedPassphrase}\""
                 + "}";
 
-        private String greeting;
-        private String name;
-        private int pageSize;
-        private List<Integer> basicRange;
-        private String storagePassphrase;
+        private final String greeting;
+        private final String name;
+        private final int pageSize;
+        private final List<Integer> basicRange;
+        private final String storagePassphrase;
 
         public AppType(
                 String name,
@@ -359,15 +381,14 @@ private static class AppTypeMapper implements Function<Config, AppType> {
 
         @Override
         public AppType apply(Config config) throws ConfigMappingException, MissingValueException {
-            AppType app = new AppType(
+
+            return new AppType(
                     config.get("name").asString().get(),
                     config.get("greeting").asString().get(),
                     config.get("page-size").asInt().get(),
                     config.get("basic-range").asList(Integer.class).get(),
                     config.get("storagePassphrase").asString().get()
             );
-
-            return app;
         }
     }
 }

config/hocon/src/test/resources/config.json

@@ -6,5 +6,9 @@
     "oracle": {
         "com": "1",
         "cz": "2"
-    }
+    },
+    "nulls": {
+        "null": null
+    },
+    "nulls-array": ["test", null]
 }