Weird customer_email attribute when using set_coupons

[michaelfranzl]

The Woocommerce user interface in Wordpress, on the Coupons page, shows a weird customer email address:

a:1:{i:0;s:0:"";}

The request I made:

{
  "action": "woocommerce_json_api",
  "proc": "set_coupons",
  "arguments": {
    "token": "1234"
  },
  "payload": [
    {
      "code": "cc4",
      "slug": "",
      "type": "shop_coupon",
      "publishing": "publish",
      "discount_type": "",
      "value": "",
      "is_exclusive": "yes",
      "limit": "",
      "product_ids": [
        ""
      ],
      "exclude_product_ids": "",
      "expiry_date": "",
      "is_before_tax": "yes",
      "is_shipping_free": "yes",
      "will_exclude_sale_products": "yes",
      "product_category_ids": [
        ""
      ],
      "exclude_product_category_ids": [
        ""
      ],
      "minimum_total": "",
      "customer_email": [
        ""
      ]
    }
  ]
}

Similarly, when I send an email address with it:

      "customer_email": [
        "m@m.com"
      ]

The backend shows:

a:1:{i:0;s:7:"m@m.com";}