[helidon] Fix for list of query parameters or form parameters

Add the test and fix for this case.

Author: rbygrave

http-generator-helidon/src/main/java/io/avaje/http/generator/helidon/nima/NimaPlatformAdapter.java

@@ -118,8 +118,8 @@ public void writeReadMapParameter(Append writer, ParamType paramType) {
   @Override
   public void writeReadCollectionParameter(Append writer, ParamType paramType, String paramName) {
     switch (paramType) {
-      case QUERYPARAM -> writer.append("queryParams.all(\"%s\")", paramName);
-      case FORMPARAM -> writer.append("formParams.all(\"%s\")", paramName);
+      case QUERYPARAM -> writer.append("queryParams.all(\"%s\", () -> java.util.List.of())", paramName);
+      case FORMPARAM -> writer.append("formParams.all(\"%s\", () -> java.util.List.of())", paramName);
 
       case HEADER -> writer.append(
           "req.headers().all(\"%s\", () -> java.util.List.of())", paramName);

tests/test-nima/src/test/java/org/example/HelloControllerTest.java

@@ -32,4 +32,15 @@ void listParamMultiple() {
     assertThat(res.statusCode()).isEqualTo(200);
     assertThat(res.body()).isEqualTo("codes:[123, 456]");
   }
+
+  @Test
+  void listParamEmpty() {
+    HttpResponse<String> res = client().request()
+      .path("listParams")
+      .GET()
+      .asPlainString();
+
+    assertThat(res.statusCode()).isEqualTo(200);
+    assertThat(res.body()).isEqualTo("codes:[]");
+  }
 }