From b0b60581d270292c0de23e0d1398db552a2e055a Mon Sep 17 00:00:00 2001
From: Sam Rawlins <srawlins@google.com>
Date: Mon, 24 Aug 2020 13:37:55 -0700
Subject: [PATCH] Improve error when FLUTTER_ROOT is missing.

This is a re-do, sort of, of #1714, which was broken in #2190.
---
 lib/src/dartdoc_options.dart | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/src/dartdoc_options.dart b/lib/src/dartdoc_options.dart
index 73448029cb..523f3b68ee 100644
--- a/lib/src/dartdoc_options.dart
+++ b/lib/src/dartdoc_options.dart
@@ -1603,6 +1603,11 @@ Future<List<DartdocOption<Object>>> createDartdocOptions(
           (option.root['topLevelPackageMeta'].valueAt(dir) as PackageMeta)
               .requiresFlutter) {
         String flutterRoot = option.root['flutterRoot'].valueAt(dir);
+        if (flutterRoot == null) {
+          // For now, return null. An error is reported in
+          // [PackageBuilder.buildPackageGraph].
+          return null;
+        }
         return p.join(flutterRoot, 'bin', 'cache', 'dart-sdk');
       }
       return defaultSdkDir.absolute.path;