Prevent Converting circular structure to JSON when POST or PUT on a document with cycling references

m3 fox@fox-laptop:~/workspace/nuxeo-js-client/lib$ git diff
diff --git i/lib/nuxeo.js w/lib/nuxeo.js
index 6b1e4d0..2eee3be 100644
--- i/lib/nuxeo.js
+++ w/lib/nuxeo.js
@@ -237,7 +237,7 @@ class Nuxeo extends Base {
       options.headers['Content-Type'] = options.headers['Content-Type'] || 'application/json';
       // do not stringify FormData
       if (typeof options.body === 'object' && !(options.body instanceof FormData)) {
-        options.body = JSON.stringify(options.body);
+        options.body = this._stringify(options.body);
       }
     }
 
@@ -250,7 +250,25 @@ class Nuxeo extends Base {
       options.url += qs.stringify(options.queryParams);
     }
     return options;
-  }
+  },
+
+  _stringify: function(obj) {
+       var cache = [];
+       var result = JSON.stringify(obj, function(key, value) {
+      if (typeof value === 'object' && value !== null) {
+        if (cache.indexOf(value) !== -1) {
+          // Circular reference found, discard key
+          return;
+        }
+        // Store value in our collection
+        cache.push(value);
+      }
+      return value;
+    });
+       // Allow GC
+    cache = null;
+    return result;
+  },