[FIX-10522] Adding nil for the optional parameters in the Swift5 model constructors similar to Swift4.

Author: Tesan3010

src/main/resources/handlebars/swift5/modelObject.mustache

@@ -25,7 +25,7 @@ public struct {{classname}}: Codable {
 {{/allVars}}
 
 {{#hasVars}}
-    public init({{#allVars}}{{name}}: {{{datatypeWithEnum}}}{{^required}}?{{/required}}{{#hasMore}}, {{/hasMore}}{{/allVars}}) {
+    public init({{#allVars}}{{name}}: {{{datatypeWithEnum}}}{{^required}}? = nil{{/required}}{{#hasMore}}, {{/hasMore}}{{/allVars}}) {
         {{#allVars}}
         self.{{name}} = {{name}}
         {{/allVars}}
@@ -84,4 +84,3 @@ public struct {{classname}}: Codable {
 {{/vendorExtensions.x-codegen-has-escaped-property-names}}{{/additionalPropertiesType}}
 
 }
-