TypeError: Can not read property 'files' of undefined

I have the following code snippet for uploading firebse storage I'm using typescript.

uploadPhoto(photo) {
//Get File
this.file = photo.files[0]; // Erro nessa linha

this.metadata = {
  'contentType': this.file.type
};

//Create a storage ref
this.storageRef = firebase.storage().ref().child('images/');

// Upload file
this.storageRef.put(this.file, this.metadata);

}

It gives the following error:

TypeError: Cannot read property 'files' of undefined