Guard against missing line information (issue 27906)

pkg/analysis_server/lib/src/edit/edit_domain.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library edit.domain;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
@@ skipping 187 matching lines @@
               errorFixes.fixes.add(fix.change);
             });
           }
         }
       }
     } else {
       CompilationUnit unit = await server.getResolvedCompilationUnit(file);
       engine.AnalysisErrorInfo errorInfo = server.getErrors(file);
       if (errorInfo != null) {
         LineInfo lineInfo = errorInfo.lineInfo;
-        int requestLine = lineInfo.getLocation(offset).lineNumber;
-        for (engine.AnalysisError error in errorInfo.errors) {
-          int errorLine = lineInfo.getLocation(error.offset).lineNumber;
-          if (errorLine == requestLine) {
-            List<Fix> fixes = await computeFixes(server.serverPlugin,
-                server.resourceProvider, unit.element.context, error);
-            if (fixes.isNotEmpty) {
-              AnalysisError serverError =
-                  newAnalysisError_fromEngine(lineInfo, error);
-              AnalysisErrorFixes errorFixes =
-                  new AnalysisErrorFixes(serverError);
-              errorFixesList.add(errorFixes);
-              fixes.forEach((fix) {
-                errorFixes.fixes.add(fix.change);
-              });
+        if (lineInfo != null) {
+          int requestLine = lineInfo.getLocation(offset).lineNumber;
+          for (engine.AnalysisError error in errorInfo.errors) {
+            int errorLine = lineInfo.getLocation(error.offset).lineNumber;
+            if (errorLine == requestLine) {
+              List<Fix> fixes = await computeFixes(server.serverPlugin,
+                  server.resourceProvider, unit.element.context, error);
+              if (fixes.isNotEmpty) {
+                AnalysisError serverError =
+                    newAnalysisError_fromEngine(lineInfo, error);
+                AnalysisErrorFixes errorFixes =
+                    new AnalysisErrorFixes(serverError);
+                errorFixesList.add(errorFixes);
+                fixes.forEach((fix) {
+                  errorFixes.fixes.add(fix.change);
+                });
+              }
             }
           }
         }
       }
     }
 
     // Send the response.
     server.sendResponse(
         new EditGetFixesResult(errorFixesList).toResponse(request.id));
   }
@@ skipping 701 matching lines @@
     }
     return new RefactoringStatus();
   }
 }
 
 /**
  * [_RefactoringManager] throws instances of this class internally to stop
  * processing in a manager that was reset.
  */
 class _ResetError {}