fix(generator): fix java.lang.NullPointerException: Cannot read field "name" because "codegenModel" is null

Author: n-rodriguez

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

@@ -745,6 +745,11 @@ private String constructExampleCode(CodegenProperty codegenProperty, HashMap<Str
 
     private String constructExampleCode(CodegenModel codegenModel, HashMap<String, CodegenModel> modelMaps,
                                         HashMap<String, Integer> processedModelMap) {
+        // fix: java.lang.NullPointerException: Cannot read field "name" because "codegenModel" is null
+        if (codegenModel == null) {
+            return "";
+        }
+
         // break infinite recursion. Return, in case a model is already processed in the
         // current context.
         String model = codegenModel.name;