fix(medusa): Delete ProductOption on Product without Variants (#1846)

**What**
Solves admin issue [166](https://github.com/medusajs/admin/issues/166)

Deleting a product option on a product without variants currently throws, because we are cleaning up variant options as well.  

**How**
Only do variant clean up, if product has variants

.changeset/twelve-pots-kneel.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/medusa": patch
+---
+
+Fixes an error thrown when deleting product options on a product without variants

integration-tests/api/__tests__/admin/product.js

@@ -12,6 +12,7 @@ const {
   MoneyAmount,
 } = require("@medusajs/medusa")
 const priceListSeeder = require("../../helpers/price-list-seeder")
+const { simpleProductFactory } = require("../../factories")
 
 jest.setTimeout(50000)
 
@@ -1433,6 +1434,58 @@ describe("/admin/products", () => {
     })
   })
 
+  describe("DELETE /admin/products/:id/options/:option_id", () => {
+    beforeEach(async () => {
+      try {
+        await simpleProductFactory(dbConnection, {
+          id: "test-product-without-variants",
+          variants: [],
+          options: [
+            {
+              id: "test-product-option",
+              title: "Test option",
+            },
+          ],
+        })
+        await adminSeeder(dbConnection)
+      } catch (err) {
+        console.log(err)
+        throw err
+      }
+    })
+
+    afterEach(async () => {
+      const db = useDb()
+      await db.teardown()
+    })
+
+    it("deletes a product option", async () => {
+      const api = useApi()
+
+      const response = await api
+        .delete(
+          "/admin/products/test-product-without-variants/options/test-product-option",
+          {
+            headers: {
+              Authorization: "Bearer test_token",
+            },
+          }
+        )
+        .catch((err) => {
+          console.log(err)
+        })
+
+      expect(response.status).toEqual(200)
+      expect(response.data.product).toEqual(
+        expect.objectContaining({
+          options: [],
+          id: "test-product-without-variants",
+          variants: [],
+        })
+      )
+    })
+  })
+
   describe("GET /admin/products/:id/variants", () => {
     beforeEach(async () => {
       await productSeeder(dbConnection)

packages/medusa/src/services/product.ts

@@ -818,32 +818,37 @@ class ProductService extends TransactionBaseService {
         return Promise.resolve()
       }
 
-      // For the option we want to delete, make sure that all variants have the
-      // same option values. The reason for doing is, that we want to avoid
-      // duplicate variants. For example, if we have a product with size and
-      // color options, that has four variants: (black, 1), (black, 2),
-      // (blue, 1), (blue, 2) and we delete the size option from the product,
-      // we would end up with four variants: (black), (black), (blue), (blue).
-      // We now have two duplicate variants. To ensure that this does not
-      // happen, we will force the user to select which variants to keep.
-      const firstVariant = product.variants[0]
+      // In case the product does not contain variants, we can safely delete the option
+      // If it does contain variants, we need to make sure no variant exist for the
+      // product option to delete
+      if (product?.variants?.length) {
+        // For the option we want to delete, make sure that all variants have the
+        // same option values. The reason for doing is, that we want to avoid
+        // duplicate variants. For example, if we have a product with size and
+        // color options, that has four variants: (black, 1), (black, 2),
+        // (blue, 1), (blue, 2) and we delete the size option from the product,
+        // we would end up with four variants: (black), (black), (blue), (blue).
+        // We now have two duplicate variants. To ensure that this does not
+        // happen, we will force the user to select which variants to keep.
+        const firstVariant = product.variants[0]
 
-      const valueToMatch = firstVariant.options.find(
-        (o) => o.option_id === optionId
-      )?.value
+        const valueToMatch = firstVariant.options.find(
+          (o) => o.option_id === optionId
+        )?.value
 
-      const equalsFirst = await Promise.all(
-        product.variants.map(async (v) => {
-          const option = v.options.find((o) => o.option_id === optionId)
-          return option?.value === valueToMatch
-        })
-      )
-
-      if (!equalsFirst.every((v) => v)) {
-        throw new MedusaError(
-          MedusaError.Types.INVALID_DATA,
-          `To delete an option, first delete all variants, such that when an option is deleted, no duplicate variants will exist.`
+        const equalsFirst = await Promise.all(
+          product.variants.map(async (v) => {
+            const option = v.options.find((o) => o.option_id === optionId)
+            return option?.value === valueToMatch
+          })
         )
+
+        if (!equalsFirst.every((v) => v)) {
+          throw new MedusaError(
+            MedusaError.Types.INVALID_DATA,
+            `To delete an option, first delete all variants, such that when an option is deleted, no duplicate variants will exist.`
+          )
+        }
       }
 
       // If we reach this point, we can safely delete the product option