The following programs compiles and runs fine on JDK6/6-open, but it fails at runtime with an IllegalArgumentException with JDK 7

import com.sun.source.util.JavacTask;
import com.sun.source.tree.*;
import java.io.IOException;
import java.net.URI;
import java.util.Arrays;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.ToolProvider;
import com.sun.tools.javac.api.JavacTrees;
import com.sun.tools.javac.tree.JCTree.*;
import com.sun.source.util.TreePath;
import com.sun.source.util.Trees;

class TestAPI {
    static class MyFileObject extends SimpleJavaFileObject {
        private String text;
        public MyFileObject(String text) {
            super(URI.create("myfo:/Test.java"), JavaFileObject.Kind.SOURCE);
            this.text = text;
        }
        @Override
        public CharSequence getCharContent(boolean ignoreEncodingErrors) {
            return text;
        }
    }
    
    public static void main(String[] args) throws IOException {
        final JavaCompiler tool = ToolProvider.getSystemJavaCompiler();

        String code = "class BadName { Object o = j; }";
        
        JavacTask ct = (JavacTask)tool.getTask(null, null, null, null, null, Arrays.asList(new MyFileObject(code)));
        
        Iterable<? extends CompilationUnitTree> compUnits = ct.parse();
CompilationUnitTree cu = compUnits.iterator().next();
ClassTree cdef = (ClassTree)cu.getTypeDecls().get(0);
JCVariableDecl vdef = (JCVariableDecl)cdef.getMembers().get(0);
TreePath path = TreePath.getPath(cu, vdef.init);
Trees.instance(ct).getScope(path);
    }
}

Output with JDK6 is:

null:0: cannot find symbol
symbol : variable j
location: class BadName

Output with JDK7 is:

Exception in thread "main" java.lang.IllegalArgumentException
        at com.sun.tools.javac.util.JCDiagnostic.<init>(JCDiagnostic.java:276)
        at com.sun.tools.javac.util.JCDiagnostic$Factory.error(JCDiagnostic.java:86)
        at com.sun.tools.javac.util.AbstractLog.error(AbstractLog.java:86)
        at com.sun.tools.javac.comp.Resolve$ResolveError.report(Resolve.java:1667)
        at com.sun.tools.javac.comp.Resolve.access(Resolve.java:1093)
        at com.sun.tools.javac.comp.Resolve.access(Resolve.java:1113)
        at com.sun.tools.javac.comp.Resolve.resolveIdent(Resolve.java:1176)
        at com.sun.tools.javac.comp.Attr.visitIdent(Attr.java:1755)
        at com.sun.tools.javac.tree.JCTree$JCIdent.accept(JCTree.java:1679)
        at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:372)
        at com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:396)
        at com.sun.tools.javac.comp.Attr.attribExprToTree(Attr.java:301)
        at com.sun.tools.javac.api.JavacTrees.attribExprToTree(JavacTrees.java:302)
        at com.sun.tools.javac.api.JavacTrees.getAttrContext(JavacTrees.java:282)
        at com.sun.tools.javac.api.JavacTrees.getScope(JavacTrees.java:199)
        at com.sun.tools.javac.api.JavacTrees.getScope(JavacTrees.java:78)
        at TestAPI.main(TestAPI.java:41)