Fix feature flagging parser coverage

Author: leoromanovsky

products/feature-flagging/feature-flagging-lib/src/main/java/com/datadog/featureflag/JsonApiUfcResponseParser.java

@@ -1,6 +1,5 @@
 package com.datadog.featureflag;
 
-import com.squareup.moshi.JsonDataException;
 import com.squareup.moshi.JsonReader;
 import datadog.trace.api.featureflag.ufc.v1.ServerConfiguration;
 import java.io.ByteArrayInputStream;
@@ -87,8 +86,7 @@ private static ServerConfiguration validConfiguration(
   }
 
   private static void requireEndOfDocument(final JsonReader reader) throws IOException {
-    if (reader.peek() != JsonReader.Token.END_DOCUMENT) {
-      throw new JsonDataException("JSON document was not fully consumed");
-    }
+    // A strict JsonReader throws if another top-level value follows the parsed document.
+    reader.peek();
   }
 }

products/feature-flagging/feature-flagging-lib/src/main/java/com/datadog/featureflag/UniversalFlagConfigParser.java

@@ -51,9 +51,8 @@ ServerConfiguration parse(final JsonReader reader) throws IOException {
   }
 
   private static void requireEndOfDocument(final JsonReader reader) throws IOException {
-    if (reader.peek() != JsonReader.Token.END_DOCUMENT) {
-      throw new JsonDataException("JSON document was not fully consumed");
-    }
+    // A strict JsonReader throws if another top-level value follows the parsed document.
+    reader.peek();
   }
 
   static final class FlagMapAdapter extends JsonAdapter<Map<String, Flag>> {

products/feature-flagging/feature-flagging-lib/src/test/java/com/datadog/featureflag/JsonApiUfcResponseParserTest.java

@@ -42,6 +42,11 @@ void rejectsUnexpectedJsonApiType() throws Exception {
     assertNull(parse("{\"data\":{\"type\":\"other-type\",\"attributes\":" + emptyConfig() + "}}"));
   }
 
+  @Test
+  void rejectsNonStringJsonApiType() throws Exception {
+    assertNull(parse("{\"data\":{\"type\":null,\"attributes\":" + emptyConfig() + "}}"));
+  }
+
   @Test
   void rejectsConfigurationWithoutFlags() throws Exception {
     assertNull(