fix dart optional params

Author: lohanidamodar

templates/dart/lib/src/models/model.dart.twig

@@ -23,7 +23,7 @@ class {{ definition.name | caseUcfirst | overrideIdentifier }} {
     factory {{ definition.name | caseUcfirst | overrideIdentifier}}.fromMap(Map<String, dynamic> map) {
         return {{ definition.name | caseUcfirst | overrideIdentifier }}(
 {% for property in definition.properties %}
-            {{ property.name | escapeKeyword }}: {% if property.sub_schema %}{% if property.type == 'array' %}List<{{property.sub_schema | caseUcfirst | overrideIdentifier}}>.from(map['{{property.name | escapeDollarSign }}'].map((p) => {{property.sub_schema | caseUcfirst | overrideIdentifier}}.fromMap(p))){% else %}{{property.sub_schema | caseUcfirst | overrideIdentifier}}.fromMap(map['{{property.name | escapeDollarSign }}']){% endif %}{% else %}map['{{property.name | escapeDollarSign }}']{% if property.type == "number" %}.toDouble(){% endif %}{% if property.type == "string" %}.toString(){% endif %}{% endif %},
+            {{ property.name | escapeKeyword }}: {% if property.sub_schema %}{% if property.type == 'array' %}List<{{property.sub_schema | caseUcfirst | overrideIdentifier}}>.from(map['{{property.name | escapeDollarSign }}'].map((p) => {{property.sub_schema | caseUcfirst | overrideIdentifier}}.fromMap(p))){% else %}{{property.sub_schema | caseUcfirst | overrideIdentifier}}.fromMap(map['{{property.name | escapeDollarSign }}']){% endif %}{% else %}map['{{property.name | escapeDollarSign }}']{% if property.type == "number" %}{% if not property.required %}?{% endif %}.toDouble(){% endif %}{% if property.type == "string" %}{% if not property.required %}?{% endif %}.toString(){% endif %}{% endif %},
 {% endfor %}
 {% if definition.additionalProperties %}
             data: map,