Add empty data param to cURL if no POST request body was given (#6017)

* Add empty data param to cURL if no request body was given

Some middleware applications do not allow POST requests without a content-length header. By adding a empty data parameter to the curl command, the content-length header will be set by curl. Besides this it is more obvious to the user that no request body is sent.

* use double quotes like the rest of the curl command

test/mocha/core/curlify.js

@@ -25,6 +25,17 @@ describe("curlify", function() {
         expect(curlified).toEqual("curl -X POST \"http://example.com\" -H  \"Accept: application/json\" -H  \"content-type: application/json\" -d {\"id\":0,\"name\":\"doggie\",\"status\":\"available\"}")
     })
 
+    it("does add a empty data param if no request body given", function() {
+      var req = {
+        url: "http://example.com",
+        method: "POST",
+      }
+
+      let curlified = curl(Im.fromJS(req))
+
+      expect(curlified).toEqual("curl -X POST \"http://example.com\" -d \"\"")
+    })
+
     it("does not change the case of header in curl", function() {
         var req = {
             url: "http://example.com",
@@ -36,7 +47,7 @@ describe("curlify", function() {
 
         let curlified = curl(Im.fromJS(req))
 
-        expect(curlified).toEqual("curl -X POST \"http://example.com\" -H  \"conTenT Type: application/Moar\"")
+        expect(curlified).toEqual("curl -X POST \"http://example.com\" -H  \"conTenT Type: application/Moar\" -d \"\"")
     })
 
     it("prints a curl statement with an array of query params", function() {
@@ -145,7 +156,7 @@ describe("curlify", function() {
 
     it("should print a curl with formData that extracts array representation with hashIdx", function() {
         // Note: hashIdx = `_**[]${counter}`
-        // Usage of hashIdx is an internal SwaggerUI method to convert formData array into something curlify can handle 
+        // Usage of hashIdx is an internal SwaggerUI method to convert formData array into something curlify can handle
         const req = {
             url: "http://example.com",
             method: "POST",