Fix serializing and deserializing empty config

Author: ogesaku

src/main/java/com/coditory/quark/config/ConfigFormat.java

@@ -2,10 +2,10 @@
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import org.snakeyaml.engine.v2.api.Dump;
 import org.snakeyaml.engine.v2.api.DumpSettings;
 import org.snakeyaml.engine.v2.api.Load;
 import org.snakeyaml.engine.v2.api.LoadSettings;
-import org.snakeyaml.engine.v2.api.Dump;
 import org.snakeyaml.engine.v2.common.FlowStyle;
 
 import java.io.ByteArrayInputStream;
@@ -93,7 +93,7 @@ public Config parse(String config) {
             LoadSettings settings = LoadSettings.builder().build();
             Load yaml = new Load(settings);
             Map<String, Object> map = (Map<String, Object>) yaml.loadFromString(config);
-            return Config.of(map);
+            return map == null || map.isEmpty() ? Config.empty() : Config.of(map);
         }
 
         @SuppressWarnings("unchecked")
@@ -107,6 +107,7 @@ public Config parse(InputStream config) {
 
         @Override
         public String stringify(Config config) {
+            if (config.isEmpty()) return "";
             DumpSettings settings = DumpSettings.builder().setDefaultFlowStyle(FlowStyle.BLOCK).build();
             Dump dump = new Dump(settings);
             dump.dumpToString(config.toMap());
@@ -123,7 +124,7 @@ private static class JsonConfigParser implements ConfigFormatParser {
         @SuppressWarnings("unchecked")
         public Config parse(String config) {
             Map<String, Object> map = gson.fromJson(config, Map.class);
-            return Config.of(map);
+            return map == null || map.isEmpty() ? Config.empty() : Config.of(map);
         }
 
         @Override
@@ -162,6 +163,7 @@ public Config parse(InputStream config) throws Exception {
 
         @Override
         public String stringify(Config config) {
+            if (config.isEmpty()) return "";
             return config.toFlatMap().entrySet().stream()
                     .map(entry -> entry.getKey() + "=" + entry.getValue())
                     .collect(joining("\n", "", "\n"));

src/main/java/com/coditory/quark/config/Preconditions.java

@@ -39,7 +39,7 @@ public static <T> T expectNonNull(T value) {
 
     public static <T> T expectNonNull(T value, String name) {
         if (value == null) {
-            String message = message("Expected non-blank string", name);
+            String message = message("Expected non-null", name);
             throw new IllegalArgumentException(message);
         }
         return value;

src/test/groovy/com/coditory/quark/config/format/ConfigJsonFormatSpec.groovy

@@ -63,4 +63,11 @@ class ConfigJsonFormatSpec extends Specification {
         then:
             result.getStringList("f") == ["F0", "F1"]
     }
+
+    def "should serialize and deserialize empty config"() {
+        expect:
+            ConfigFactory.parseJson("") == Config.empty()
+        and:
+            ConfigFormatter.toJson(Config.empty()) == "{}"
+    }
 }

src/test/groovy/com/coditory/quark/config/format/ConfigPropertiesFormatSpec.groovy

@@ -58,4 +58,11 @@ class ConfigPropertiesFormatSpec extends Specification {
         then:
             result.getStringList("f") == ["F0", "F1"]
     }
+
+    def "should serialize and deserialize empty config"() {
+        expect:
+            ConfigFactory.parseProperties("") == Config.empty()
+        and:
+            ConfigFormatter.toProperties(Config.empty()) == ""
+    }
 }

src/test/groovy/com/coditory/quark/config/format/ConfigYamlFormatSpec.groovy

@@ -61,4 +61,11 @@ class ConfigYamlFormatSpec extends Specification {
         then:
             result.getStringList("f") == ["F0", "F1"]
     }
+
+    def "should serialize and deserialize empty config"() {
+        expect:
+            ConfigFactory.parseYaml("") == Config.empty()
+        and:
+            ConfigFormatter.toYaml(Config.empty()) == ""
+    }
 }