fix: [go-feature-flag] Make flag metadata optional (#572)

Signed-off-by: itchyny <[email protected]>
Co-authored-by: Thomas Poignant <[email protected]>

Author: itchyny

providers/go-feature-flag/src/main/java/dev/openfeature/contrib/providers/gofeatureflag/GoFeatureFlagProvider.java

@@ -395,6 +395,9 @@ private ErrorCode mapErrorCode(String errorCode) {
      */
     private ImmutableMetadata convertFlagMetadata(Map<String, Object> flagMetadata) {
         ImmutableMetadata.ImmutableMetadataBuilder builder = ImmutableMetadata.builder();
+        if (flagMetadata == null) {
+            return builder.build();
+        }
         flagMetadata.forEach((k, v) -> {
             if (v instanceof Long) {
                 builder.addLong(k, (Long) v);

providers/go-feature-flag/src/test/java/dev/openfeature/contrib/providers/gofeatureflag/GoFeatureFlagProviderTest.java

@@ -701,6 +701,23 @@ void should_not_fail_if_receive_an_unknown_field_in_response() {
         assertEquals(want, got);
     }
 
+    @SneakyThrows
+    @Test
+    void should_not_fail_if_no_metadata_in_response() {
+        GoFeatureFlagProvider g = new GoFeatureFlagProvider(GoFeatureFlagProviderOptions.builder().endpoint(this.baseUrl.toString()).timeout(1000).build());
+        String providerName = this.testName;
+        OpenFeatureAPI.getInstance().setProviderAndWait(providerName, g);
+        Client client = OpenFeatureAPI.getInstance().getClient(providerName);
+        FlagEvaluationDetails<Boolean> got = client.getBooleanDetails("no_metadata",false, this.evaluationContext);
+        FlagEvaluationDetails<Boolean> want = FlagEvaluationDetails.<Boolean>builder()
+                .value(true)
+                .variant("True")
+                .flagKey("no_metadata")
+                .reason(Reason.TARGETING_MATCH.name())
+                .build();
+        assertEquals(want, got);
+    }
+
     @SneakyThrows
     @Test
     void should_publish_events() {

providers/go-feature-flag/src/test/resources/mock_responses/no_metadata.json

@@ -0,0 +1,9 @@
+{
+  "trackEvents": true,
+  "variationType": "True",
+  "failed": false,
+  "version": 0,
+  "reason": "TARGETING_MATCH",
+  "errorCode": "",
+  "value": true
+}