Added a check to GSON serializer to behave consistently with all other serializers

Author: onufryk

core-api/src/main/java/com/optimizely/ab/config/parser/GsonConfigParser.java

@@ -33,6 +33,12 @@ final class GsonConfigParser implements ConfigParser {
 
     @Override
     public ProjectConfig parseProjectConfig(@Nonnull String json) throws ConfigParseException {
+        if (json == null) {
+            throw new ConfigParseException("Unable to parse null datafile.");
+        }
+        if (json.length() == 0) {
+            throw new ConfigParseException("Unable to parse empty datafile.");
+        }
         Gson gson = new GsonBuilder()
             .registerTypeAdapter(ProjectConfig.class, new ProjectConfigGsonDeserializer())
             .registerTypeAdapter(Audience.class, new AudienceGsonDeserializer())

core-api/src/test/java/com/optimizely/ab/config/parser/GsonConfigParserTest.java

@@ -22,8 +22,6 @@
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
-import static junit.framework.Assert.assertNull;
-
 
 import static com.optimizely.ab.config.ProjectConfigTestUtils.validConfigJsonV1;
 import static com.optimizely.ab.config.ProjectConfigTestUtils.validProjectConfigV1;
@@ -92,22 +90,24 @@ public void validJsonRequiredFieldMissingExceptionWrapping() throws Exception {
 
     /**
      * Verify that empty string JSON results in a {@link ConfigParseException} being thrown.
-     * This serializer doesn't throw exceptions on null or empty string
      */
     @Test
     public void emptyJsonExceptionWrapping() throws Exception {
+        thrown.expect(ConfigParseException.class);
+
         GsonConfigParser parser = new GsonConfigParser();
-        assertNull(parser.parseProjectConfig(""));
+        parser.parseProjectConfig("");
     }
 
     /**
      * Verify that null JSON results in a {@link ConfigParseException} being thrown.
-     * This serializer doesn't throw exceptions on null or empty string
      */
     @Test
     @SuppressFBWarnings(value="NP_NONNULL_PARAM_VIOLATION", justification="Testing nullness contract violation")
     public void nullJsonExceptionWrapping() throws Exception {
+        thrown.expect(ConfigParseException.class);
+
         GsonConfigParser parser = new GsonConfigParser();
-        assertNull(parser.parseProjectConfig(null));
+        parser.parseProjectConfig(null);
     }
 }