if else in react native

I am new to react native. I Have created a screen where I am using if else in function like this.

constructor(props) {
    super(props);
    this.state={
     phpid = ''
}
}

validateInputs = (event) => {
  
  const data = this.props.route.params.data
  const { phpid } = this.state;


if (data.retail_information_data[0] != '') {
      phpid == data.retail_information_data[0].id  
}else{
      phpid == null
}
 
    AsyncStorage.multiGet(["application_id", "created_by"]).then(response => {
  
       console.log(phpid)

  fetch('https://njdnfech/Android_API_CI/uploaddata/tffmerchant_retail_details?query=', {
    
      body: JSON.stringify([{phpid : phpid}])
    })
    .then((returnValue) => returnValue.json())
    .then(function(response) {
     console.log(response)
      return response.json();
}
  

but I am getting = data.retail_information_data[0] = null or lets say empty then according to if else my else condition that is 'phpid == null' shuld run but even 'data.retail_information_data[0] = null' my else condition not running my console kepp saying 'TypeError: undefined is not an object (evaluating 'data.retail_information_data[0].id')' is any problem in my if else or how to write proper if else