code: protected Object findValue(String expr) {
      if (expr == null) { return null; }
      expr = stripExpressionIfAltSyntax(expr);
      return stack.findValue(expr, false);
    }
docs: Finds a value from the OGNL stack based on the given expression. Will
  always evaluate <code>expr</code> against stack except when <code>expr</code> is null. If
  altsyntax (%{...}) is applied, simply strip
  it off.
  
  @param expr
  the expression. Returns <tt>null</tt> if expr is null.
  @return the value, <tt>null</tt> if not found.