public static boolean isValid(String param) {
        if (param == null) {
            return false;
        }
        int length = param.length();
        for (int i = 0; i < length; i++) {
            char ch = param.charAt(i);
            if (!Character.isLetterOrDigit(ch) && !isValidChar(ch)) {
                return false;
            }
        }
        return true;
    }
@Test
    void testIsValid() {
        String content = "abcABC09.:_-";
        assertTrue(ParamUtils.isValid(content));
        
        content = null;
        assertFalse(ParamUtils.isValid(content));
        
        content = "@";
        assertFalse(ParamUtils.isValid(content));
        
        content = "+";
        assertFalse(ParamUtils.isValid(content));
        
        content = "/";
        assertFalse(ParamUtils.isValid(content));
    }