feat(better fastboot compat) render in place in Fastboot

addon/components/ember-popper.js

@@ -22,6 +22,8 @@ export default Ember.Component.extend({
   // Classes to be applied to the popper element
   popperClass: null,
 
+  // The popper element needs to be moved higher in the DOM tree to avoid z-index issues.
+  // See the block-comment in the template for more details.
   popperContainer: Ember.computed({
     set(_, value) {
       if (value instanceof Element) {
@@ -38,16 +40,30 @@ export default Ember.Component.extend({
     },
 
     get() {
-      // The popper element needs to be moved higher in the DOM tree to avoid z-index issues.
-      // See the block-comment in the template for more details.
+      // There is no self.document in Fastboot, so we cannot access the document body. We avoid this
+      // issue by always rendering in place when in Fastboot.
       return self.document ? self.document.body : '';
     }
   }),
 
   // If `true`, the popper element will not be moved to popperContainer. WARNING: This can cause
   // z-index issues where your popper will be overlapped by DOM elements that aren't nested as
   // deeply in the DOM tree.
-  renderInPlace: false,
+  renderInPlace: Ember.computed({
+    set(_, value) {
+      // self.document is undefined in Fastboot, so we always render in place when it is undefined.
+      if (self.document) {
+        return value;
+      }
+
+      return true;
+    },
+
+    get() {
+      // self.document is undefined in Fastboot, so we always render in place when it is undefined.
+      return self.document ? false : true;
+    }
+  }),
 
   // The element the popper will target. If left blank, will be set to the ember-popper's parent.
   target: null,