Fix exception in stack trace from issue 23348

pkg/analysis_server/lib/src/analysis_server.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 analysis.server;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:math' show max;
 
@@ skipping 407 matching lines @@
   }
 
   /**
    * Return the primary [ContextSourcePair] representing the given [path].
    *
    * The [AnalysisContext] of this pair will be the context that explicitly
    * contains the path, if any such context exists, otherwise it will be the
    * first context that implicitly analyzes it.
    *
    * If the [path] is not analyzed by any context, a [ContextSourcePair] with
-   * `null` context and `file` [Source] is returned.
+   * a `null` context and `file` [Source] is returned.
    *
-   * If the [path] dosn't represent a file, `null` is returned as a [Source].
+   * If the [path] dosn't represent a file, a [ContextSourcePair] with a `null`
+   * context and `null` [Source] is returned.
    *
    * Does not return `null`.
    */
   ContextSourcePair getContextSourcePair(String path) {
     // try SDK
     {
       Uri uri = resourceProvider.pathContext.toUri(path);
       Source sdkSource = defaultSdk.fromFileUri(uri);
       if (sdkSource != null) {
         AnalysisContext anyContext = folderMap.values.first;
         return new ContextSourcePair(anyContext, sdkSource);
       }
     }
     // try to find the deep-most containing context
     Resource resource = resourceProvider.getResource(path);
-    File file = resource is File ? resource : null;
+    if (resource is! File) {
+      return new ContextSourcePair(null, null);
+    }
+    File file = resource;
     {
       AnalysisContext containingContext = getContainingContext(path);
       if (containingContext != null) {
-        Source source = file != null
-            ? ContextManager.createSourceInContext(containingContext, file)
-            : null;
+        Source source =
+            ContextManager.createSourceInContext(containingContext, file);
         return new ContextSourcePair(containingContext, source);
       }
     }
     // try to find a context that analysed the file
     for (AnalysisContext context in folderMap.values) {
-      Source source = file != null
-          ? ContextManager.createSourceInContext(context, file)
-          : null;
+      Source source = ContextManager.createSourceInContext(context, file);
       SourceKind kind = context.getKindOf(source);
       if (kind != SourceKind.UNKNOWN) {
         return new ContextSourcePair(context, source);
       }
     }
     // try to find a context for which the file is a priority source
     for (InternalAnalysisContext context in folderMap.values) {
       List<Source> sources = context.getSourcesWithFullName(path);
       if (sources.isNotEmpty) {
         Source source = sources.first;
         return new ContextSourcePair(context, source);
       }
     }
     // file-based source
-    Source fileSource = file != null ? file.createSource() : null;
+    Source fileSource = file.createSource();
     return new ContextSourcePair(null, fileSource);
   }
 
   /**
    * Returns [Element]s at the given [offset] of the given [file].
    *
    * May be empty if cannot be resolved, but not `null`.
    */
   List<Element> getElementsAtOffset(String file, int offset) {
     List<AstNode> nodes = getNodesAtOffset(file, offset);
@@ skipping 1013 matching lines @@
   /**
    * The [PerformanceTag] for time spent in server request handlers.
    */
   static PerformanceTag serverRequests = new PerformanceTag('serverRequests');
 
   /**
    * The [PerformanceTag] for time spent in split store microtasks.
    */
   static PerformanceTag splitStore = new PerformanceTag('splitStore');
 }