message: users - phone numbers - accept null or empty string as well
diff: "mobile": {
  "type": "string",
  "sanitize": "mongo",
  - "pattern": "^\\+?([0-9] ?){9,14}[0-9]$"
  + "pattern": "^|\\+?([0-9] ?){9,14}[0-9]$",
  + "nullable": true
  },
  "locale": {
  "type": "string",
  "phone": {
  "type": "string",
  "sanitize": "mongo",
  - "pattern": "^\\+?([0-9] ?){9,14}[0-9]$"
  + "pattern": "^|\\+?([0-9] ?){9,14}[0-9]$",
  + "nullable": true
  },
  "issuer": {
  "type": "boolean",
  