Fixing StringIndexOutOfBoundsException

I'm not really sure what this code is doing or what ID is supposed to look like. So this is just a minimum-intrusion change to avoid an exception.

java.lang.StringIndexOutOfBoundsException: String index out of range: -1
        at java.lang.String.substring(String.java:1875)
        at hudson.tasks.junit.PackageResult.findCorrespondingResult(PackageResult.java:86)
        at hudson.tasks.junit.TestResult.findCorrespondingResult(TestResult.java:295)
        at hudson.tasks.test.AbstractTestResultAction.findCorrespondingResult(AbstractTestResultAction.java:183)
        at hudson.tasks.test.TestResult.getResultInBuild(TestResult.java:162)
        at hudson.tasks.junit.History.getList(History.java:82)
        at hudson.tasks.junit.History$1.createDataSet(History.java:105)
        at hudson.tasks.junit.History$GraphImpl.createGraph(History.java:169)
        at hudson.util.Graph.render(Graph.java:87)
        at hudson.util.Graph.doPng(Graph.java:98)

core/src/main/java/hudson/tasks/junit/PackageResult.java

@@ -82,15 +82,16 @@ public final class PackageResult extends MetaTabulatedResult implements Comparab
     @Override
     public TestResult findCorrespondingResult(String id) {
         String myID = safe(getName());
+
         int base = id.indexOf(myID);
-        String className;
-        String subId = null;
+        String className = id; // fall back value
         if (base > 0) {
             int classNameStart = base + myID.length() + 1;
-            className = id.substring(classNameStart);
-        } else {
-            className = id;
-    }
+            if (classNameStart<id.length())
+                className = id.substring(classNameStart);
+        }
+
+        String subId = null;
         int classNameEnd = className.indexOf('/');
         if (classNameEnd > 0) {
             subId = className.substring(classNameEnd + 1);
@@ -106,7 +107,7 @@ public final class PackageResult extends MetaTabulatedResult implements Comparab
                 return child.findCorrespondingResult(subId);
             } else {
                 return child;
-    }
+            }
         }
 
         return null;

core/src/main/java/hudson/tasks/test/TestObject.java

@@ -138,7 +138,7 @@ public abstract class TestObject extends hudson.tasks.junit.TestObject {
         StringBuilder buf = new StringBuilder();
         TestObject next = this;
         TestObject cur = this;  
-        // Walk up my ancesotors from leaf to root, looking for "it"
+        // Walk up my ancestors from leaf to root, looking for "it"
         // and accumulating a relative url as I go
         while (next!=null && it!=next) {
             cur = next;
@@ -260,7 +260,7 @@ public abstract class TestObject extends hudson.tasks.junit.TestObject {
 
     /**
      * Find the test result corresponding to the one identified by <code>id></code>
-     * withint this test result.
+     * within this test result.
      *
      * @param id The path to the original test result
      * @return A corresponding test result, or null if there is no corresponding