php - Unexpected end of JSON input at JSON.parse

I made my RESTful mysql backend everything is good except that my feteched query has problem.I mean ,it show me nothing when my returned json is more than 2 objects. I'm working with ionic3 / http.

my select.php:

$sql = "SELECT * FROM products ORDER BY id";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    // output data of each row
     $data = array() ;
    while($row = $result->fetch_assoc()) {
        $data[] = $row;
    }
    echo json_encode($data);
} else {
    echo "0";
}
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my service file in ionic:

getProducts(){
    return this.http.get("http://localhost/api/products/select.php")
    .map(res=>{
      this.checkMe = res;

      if(this.checkMe._body !== "0"){
         return res.json()
      }

    } );
  }
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I realy need your help. Thank you all.