code: private InstalledFeature getInstalledFeatureFromCache(String feature, String namespace)
      {
          if (feature == null) {
              return null;
          }
  
          Map<String, InstalledFeature> installedExtensionsForFeature = this.extensionNamespaceByFeature.get(feature);
  
          if (installedExtensionsForFeature == null) {
              return null;
          }
  
          InstalledFeature installedExtension = installedExtensionsForFeature.get(namespace);
  
          // Fallback on root namespace if the feature could not be found
          if (installedExtension == null && namespace != null) {
              installedExtension = getInstalledFeatureFromCache(feature, null);
          }
  
          return installedExtension;
      }
docs: Get extension registered as installed for the provided feature and namespace (including on root namespace).
  
  @param feature the feature provided by the extension
  @param namespace the namespace where the extension is installed
  @return the installed extension informations