diff --git a/packages/medusa-core-utils/src/errors.js b/packages/medusa-core-utils/src/errors.js
index f5a99fd548..eae11818fc 100644
--- a/packages/medusa-core-utils/src/errors.js
+++ b/packages/medusa-core-utils/src/errors.js
@@ -7,7 +7,8 @@ export const MedusaErrorTypes = {
   DB_ERROR: "database_error",
   INVALID_ARGUMENT: "invalid_argument",
   INVALID_DATA: "invalid_data",
-  NOT_FOUND: "not_found"
+  NOT_FOUND: "not_found",
+  NOT_ALLOWED: "not_allowed"
 }
 
 /**
diff --git a/packages/medusa/src/models/customer.js b/packages/medusa/src/models/customer.js
index 349d836c7d..8aa7774161 100644
--- a/packages/medusa/src/models/customer.js
+++ b/packages/medusa/src/models/customer.js
@@ -13,7 +13,7 @@ class CustomerModel extends BaseModel {
     email: { type: String, required: true, unique: true },
     first_name: { type: String, required: true },
     last_name: { type: String, required: true },
-    billingAddress: { type: AddressSchema },
+    billing_address: { type: AddressSchema },
     password_hash: { type: String },
     metadata: { type: mongoose.Schema.Types.Mixed, default: {} },
   }
diff --git a/packages/medusa/src/services/cart.js b/packages/medusa/src/services/cart.js
index 19355481a7..b206f4eb63 100644
--- a/packages/medusa/src/services/cart.js
+++ b/packages/medusa/src/services/cart.js
@@ -172,7 +172,10 @@ class CartService extends BaseService {
   }
 
   /**
-   *
+   * Adds a line item to the cart.
+   * @param {string} cartId - the id of the cart that we will add to
+   * @param {LineItem} lineItem - the line item to add.
+   * @retur {Promise} the result of the update operation
    */
   async addLineItem(cartId, lineItem) {
     const validatedLineItem = this.validateLineItem_(lineItem)