[C][Client] Fix default enum value being -1 (#18040)

Author: bookerdj

modules/openapi-generator/src/main/resources/C-libcurl/model-body.mustache

@@ -845,7 +845,7 @@ fail:
         {{^isPrimitiveType}}
         {{#isModel}}
         {{#isEnum}}
-        {{^required}}{{{name}}} ? {{/required}}{{{name}}}_local_nonprim_enum{{^required}} : -1{{/required}}{{^-last}},{{/-last}}
+        {{^required}}{{{name}}} ? {{/required}}{{{name}}}_local_nonprim_enum{{^required}} : {{projectName}}_{{classVarName}}_{{enumName}}_NULL{{/required}}{{^-last}},{{/-last}}
         {{/isEnum}}
         {{^isEnum}}
         {{^required}}{{{name}}} ? {{/required}}{{{name}}}_local_nonprim{{^required}} : NULL{{/required}}{{^-last}},{{/-last}}
@@ -875,7 +875,7 @@ fail:
         {{/isBoolean}}
         {{#isEnum}}
         {{#isString}}
-        {{^required}}{{{name}}} ? {{/required}}{{name}}Variable{{^required}} : -1{{/required}}{{^-last}},{{/-last}}
+        {{^required}}{{{name}}} ? {{/required}}{{name}}Variable{{^required}} : {{projectName}}_{{classVarName}}_{{enumName}}_NULL{{/required}}{{^-last}},{{/-last}}
         {{/isString}}
         {{/isEnum}}
         {{^isEnum}}

samples/client/petstore/c/model/order.c

@@ -182,7 +182,7 @@ order_t *order_parseFromJSON(cJSON *orderJSON){
         pet_id ? pet_id->valuedouble : 0,
         quantity ? quantity->valuedouble : 0,
         ship_date && !cJSON_IsNull(ship_date) ? strdup(ship_date->valuestring) : NULL,
-        status ? statusVariable : -1,
+        status ? statusVariable : openapi_petstore_order_STATUS_NULL,
         complete ? complete->valueint : 0
         );
 

samples/client/petstore/c/model/pet.c

@@ -263,7 +263,7 @@ pet_t *pet_parseFromJSON(cJSON *petJSON){
         strdup(name->valuestring),
         photo_urlsList,
         tags ? tagsList : NULL,
-        status ? statusVariable : -1
+        status ? statusVariable : openapi_petstore_pet_STATUS_NULL
         );
 
     return pet_local_var;