ogcapi's geo+json output formats cause NPE when request comes from WFS

ogc-features introduce two GeoJSON output formats:
- RFCGeoJSONFeaturesResponse
- DGGSGeoJSONResponse

As such, they're listed in WFS GetCapabilities as GetFeature
operation's output formats, besides the usual 'application/json'
one.

When feature collection is requested through WFS with output
format application/geo+json, an NPE exeption is thrown once
it streamed the features and calls writeLinks(), resulting
in an XML exception report mixed up with the JSON output.

This patch checks whether APIRequestInfo.get() returns null,
which means the response being produced by these new encoders
is not coming from an ogc-api endpoint, and avoids using
APIRequestInfo to write json links.

src/community/ogcapi/ogcapi-core/src/main/java/org/geoserver/api/APIRequestInfo.java

@@ -76,7 +76,10 @@ String buildURI(String base, String path) {
         return ResponseUtils.buildURL(baseURL, path, null, URLMangler.URLType.SERVICE);
     }
 
-    /** Returns the APIRequestInfo from the current {@link RequestContextHolder} */
+    /**
+     * Returns the APIRequestInfo from the current {@link RequestContextHolder}, or {@code null}
+     * indicating there's no OGC API request bound to the calling thread
+     */
     public static APIRequestInfo get() {
         RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
         if (requestAttributes == null) return null;

src/community/ogcapi/ogcapi-features/src/main/java/org/geoserver/api/features/RFCGeoJSONFeaturesResponse.java

@@ -111,6 +111,10 @@ private void writeLinks(
             GeoJSONBuilder jw,
             String featureId) {
         APIRequestInfo requestInfo = APIRequestInfo.get();
+        if (null == requestInfo) {
+            // request comes from WFS, not from ogcapi
+            return;
+        }
         GetFeatureRequest request = GetFeatureRequest.adapt(operation.getParameters()[0]);
         FeatureTypeInfo featureType = getFeatureType(request);
         String baseUrl = request.getBaseUrl();