#fixed code
                              private static boolean hasCallHandlerMethod( Class rootClass )
  {
    if( ICallHandler.class.isAssignableFrom( rootClass ) )
    {
      // Nominally implements ICallHandler
      return true;
    }
    if( ReflectUtil.method( rootClass, "call", Class.class, String.class, String.class, Class.class, Class[].class, Object[].class ) != null )
    {
      // Structurally implements ICallHandler
      return true;
    }

    // maybe has an extension satisfying ICallHandler
    return hasCallHandlerFromExtension( rootClass );
  }
#vulnerable code 
                              private static boolean hasCallHandlerMethod( Class rootClass )
  {
    String fqn = rootClass.getCanonicalName();
    BasicJavacTask javacTask = RuntimeManifoldHost.get().getJavaParser().getJavacTask();
    Pair<Symbol.ClassSymbol, JCTree.JCCompilationUnit> classSymbol = ClassSymbols.instance( RuntimeManifoldHost.get().getSingleModule() ).getClassSymbol( javacTask, fqn );
    Pair<Symbol.ClassSymbol, JCTree.JCCompilationUnit> callHandlerSymbol = ClassSymbols.instance( RuntimeManifoldHost.get().getSingleModule() ).getClassSymbol( javacTask, ICallHandler.class.getCanonicalName() );
    if( Types.instance( javacTask.getContext() ).isAssignable( classSymbol.getFirst().asType(), callHandlerSymbol.getFirst().asType() ) )
    {
      // Nominally implements ICallHandler
      return true;
    }

    return hasCallMethod( javacTask, classSymbol.getFirst() );
  } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE