Ensure @JsonSerialize and @JsonDeserialize is only generated when Jackson enabled

Fixes #6496

Author: Philzen

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java

@@ -1779,7 +1779,7 @@ private void addAdditionalImports(CodegenModel model, CodegenComposedSchemas com
 
     @Override
     public void postProcessModelProperty(CodegenModel model, CodegenProperty property) {
-        if (serializeBigDecimalAsString) {
+        if (serializeBigDecimalAsString && additionalProperties.containsKey(JACKSON)) {
             if ("decimal".equals(property.baseType) || "bigdecimal".equalsIgnoreCase(property.baseType)) {
                 // we serialize BigDecimal as `string` to avoid precision loss
                 property.vendorExtensions.put("x-extra-annotation", "@JsonSerialize(using = ToStringSerializer.class)");
@@ -1804,7 +1804,7 @@ public void postProcessModelProperty(CodegenModel model, CodegenProperty propert
             model.imports.add("Arrays");
         } else if ("set".equals(property.containerType)) {
             model.imports.add("LinkedHashSet");
-            if (!openApiNullable || !property.isNullable) { // cannot be wrapped to nullable
+            if ((!openApiNullable || !property.isNullable) && additionalProperties.containsKey(JACKSON)) { // cannot be wrapped to nullable
                 model.imports.add("JsonDeserialize");
                 property.vendorExtensions.put("x-setter-extra-annotation", "@JsonDeserialize(as = LinkedHashSet.class)");
             }