message: make fields in address nullable
diff: #[derive(Debug, Deserialize, Serialize)]
  pub struct Address {
  - pub line1: String,
  - pub line2: String,
  - pub city: String,
  - pub state: String,
  - pub postal_code: String,
  - pub country: String,
  + pub line1: Option<String>,
  + pub line2: Option<String>,
  + pub city: Option<String>,
  + pub state: Option<String>,
  + pub postal_code: Option<String>,
  + pub country: Option<String>,
  }
  