fix(webshipper): only add invoices if invoice generator produces a file (#1749)

packages/medusa-fulfillment-webshipper/src/services/webshipper-fulfillment.js

@@ -287,19 +287,21 @@ class WebshipperFulfillmentService extends FulfillmentService {
           fulfillmentItems
         )
 
-        invoice = await this.client_.documents
-          .create({
-            type: "documents",
-            attributes: {
-              document_size: this.options_.document_size || "A4",
-              document_format: "PDF",
-              base64: base64Invoice,
-              document_type: "invoice",
-            },
-          })
-          .catch((err) => {
-            throw err
-          })
+        if (base64Invoice) {
+          invoice = await this.client_.documents
+            .create({
+              type: "documents",
+              attributes: {
+                document_size: this.options_.document_size || "A4",
+                document_format: "PDF",
+                base64: base64Invoice,
+                document_type: "invoice",
+              },
+            })
+            .catch((err) => {
+              throw err
+            })
+        }
 
         const cooCountries = this.options_.coo_countries
         if (