Fix throwing ObjectNotClosure instead of null exception if closure is null.

corelib/src/expect.dart

 // Copyright (c) 2011, 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.
 
 class Expect {
 
   /**
    * Checks whether the expected and actual values are equal (using [:==:]).
    */
   static void equals(var expected, var actual, [String reason = null]) {
@@ skipping 109 matching lines @@
   /**
    * Specialized equality test for strings. When the strings don't match,
    * this method shows where the mismatch starts and ends.
    */
   static void stringEquals(String expected,
                            String actual,
                            [String reason = null]) {
     String msg = _getMessage(reason);
     String defaultMessage =
         'Expect.stringEquals(expected: <$expected>", <$actual>$msg) fails';
-    if (expected != actual) {
-      // scan from the left until we find a mismatch
-      int left = 0;
-      int eLen = expected.length;
-      int aLen = actual.length;
-      while (true) {
-        if (left == eLen) {
-          assert (left < aLen);
-          String snippet = actual.substring(left, aLen);
-          _fail('$defaultMessage\nDiff:\n...[  ]\n...[ $snippet ]');
-          return;
-        }
-        if (left == aLen) {
-          assert (left < eLen);
-          String snippet = expected.substring(left, eLen);
-          _fail('$defaultMessage\nDiff:\n...[  ]\n...[ $snippet ]');
-          return;
-        }
-        if (expected[left] != actual[left]) {
-          break;
-        }
-        left++;
+
+    if (expected == actual) return;
+    if ((expected === null) || (actual === null)) {
+      _fail('$defaultMessage');
+    }
+    // scan from the left until we find a mismatch
+    int left = 0;
+    int eLen = expected.length;
+    int aLen = actual.length;
+    while (true) {
+      if (left == eLen) {
+        assert (left < aLen);
+        String snippet = actual.substring(left, aLen);
+        _fail('$defaultMessage\nDiff:\n...[  ]\n...[ $snippet ]');
+        return;
       }
+      if (left == aLen) {
+        assert (left < eLen);
+        String snippet = expected.substring(left, eLen);
+        _fail('$defaultMessage\nDiff:\n...[  ]\n...[ $snippet ]');
+        return;
+      }
+      if (expected[left] != actual[left]) {
+        break;
+      }
+      left++;
+    }
 
-      // scan from the right until we find a mismatch
-      int right = 0;
-      while (true) {
-        if (right == eLen) {
-          assert (right < aLen);
-          String snippet = actual.substring(0, aLen - right);
-          _fail('$defaultMessage\nDiff:\n[  ]...\n[ $snippet ]...');
-          return;
-        }
-        if (right == aLen) {
-          assert (right < eLen);
-          String snippet = expected.substring(0, eLen - right);
-          _fail('$defaultMessage\nDiff:\n[  ]...\n[ $snippet ]...');
-          return;
-        }
-        if (expected[eLen - right - 1] != actual[aLen - right - 1]) {
-          break;
-        }
-        right++;
+    // scan from the right until we find a mismatch
+    int right = 0;
+    while (true) {
+      if (right == eLen) {
+        assert (right < aLen);
+        String snippet = actual.substring(0, aLen - right);
+        _fail('$defaultMessage\nDiff:\n[  ]...\n[ $snippet ]...');
+        return;
       }
-
-      String eSnippet = expected.substring(left, eLen - right);
-      String aSnippet = actual.substring(left, aLen - right);
-      String diff = '\nDiff:\n...[ $eSnippet} ]...\n...[ $aSnippet ]...';
-      _fail('$defaultMessage$diff');
+      if (right == aLen) {
+        assert (right < eLen);
+        String snippet = expected.substring(0, eLen - right);
+        _fail('$defaultMessage\nDiff:\n[  ]...\n[ $snippet ]...');
+        return;
+      }
+      if (expected[eLen - right - 1] != actual[aLen - right - 1]) {
+        break;
+      }
+      right++;
     }
+    String eSnippet = expected.substring(left, eLen - right);
+    String aSnippet = actual.substring(left, aLen - right);
+    String diff = '\nDiff:\n...[ $eSnippet} ]...\n...[ $aSnippet ]...';
+    _fail('$defaultMessage$diff');
   }
 
   /**
    * Checks that every element of [expected] is also in [actual], and that
    * every element of [actual] is also in [expected].
    */
   static void setEquals(Iterable expected,
                         Iterable actual,
                         [String reason = null]) {
     final missingSet = new Set.from(expected);
@@ skipping 59 matching lines @@
   }
 }
 
 typedef bool _CheckExceptionFn(exception);
 
 class ExpectException implements Exception {
   ExpectException(this.message);
   String toString() => message;
   String message;
 }