Angular 6 and PHP looping over json array sent through HttPClient giving invalid argument in foreach loop

I am sending an array with other data using HttpClient of angular 6.

And as it's mentioned in this post on github, sending arrays with HttpClient is still not available, so I had a problem reading arrays when received in PHP and var_dump showed me null objects.

I found a solution by transforming the array into JSON using json.stringify(array) and it worked, as the received array is properly shown in var_dump:

this.auth.saveUnitData(
  unit_type, 
  location_id,
  user, 
  number_of, 
  status, 
  add_date, 
  JSON.stringify(arrayOfActualities))
  .subscribe(
    (data)=>{
      console.log(data);
    },
    (error)=>{
      console.log(error);
    }
  )

var_dump() result:

(
    [unit_type] => 1

    [location_id] => 1

    [user] => 1

    [number_of] => 2

    [status] => Active

    [add_date] => 2018-09-13

    [arrayOfActualities] => 

[{"legalId":"","protectionId":"1","situationId":"","addDate":"2018-09-13"}]

)

In the PHP code and as sometimes a foreign key could be null as one of actualities sent through the array does not exist, I wrote the following script:

$arrayOfActualities = json_encode($arrayOfActualities);
if(sizeof($arrayOfActualities)>0)
{
    foreach($arrayOfActualities as $array)
    {
        if($array['situationId']==="")
        {
            $situation_id=null;
        }
        else{
            $situation_id = $array['situationId'];
        }
        if($array['legalId']==="")
        {
            $legal_id=null;
        }
        else{
            $legal_id = $array['legalId'];
        }
        if($array['protectionId']==="")
        {
            $protection_id=null;
        }
        else{
            $protection_id = $array['protectionId'];
        }

        $status = "Active";

        try{
            $sqlActualities = "INSERT into unit_situation_legal_protection( 
            unit_situation_legal_protection_status, 
            unit_situation_legal_protection_date_added, 
            legal_id, situation_id, protection_id, user_id)
                                VALUES(:actStatus, :dateAdded, :legal,
                                        :situation, :protection, :userId)";
            $sqlActExec = $this->conn->prepare($sqlActualities);
            $sqlActExec->bindValue('actStatus', $status);
            $sqlActExec->bindValue('dateAdded', $dateAdded);
            $sqlActExec->bindValue('legal', $legal_id);
            $sqlActExec->bindValue('situation', $situation_id);
            $sqlActExec->bindValue('protection', $protection_id);
            $sqlActExec->bindValue('userId', $user_id);
            $sqlActExec->execute();

            return "success";
        }
        catch(PDOException $e)
        {
            return $e->getMessage();
        }
    }        
}

The problem is that nothing of the actualities are added to the database, and it's showing me the following error:

Warning: Invalid argument supplied for foreach()

So, if I changed to:

foreach(json_decode($arrayOfActualities) as $array)

I got the following error:

Invalid value of '['

I think this error because the array transformed into json and a [ was added before each row of the json, so php thought it's a value or something.