Make ClassModel immutable

JAVA-3364

Author: jstewart148

bson/src/main/org/bson/codecs/pojo/ClassModel.java

@@ -16,6 +16,7 @@
 
 package org.bson.codecs.pojo;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 
@@ -44,13 +45,13 @@ public final class ClassModel<T> {
         this.name = clazz.getSimpleName();
         this.type = clazz;
         this.hasTypeParameters = clazz.getTypeParameters().length > 0;
-        this.propertyNameToTypeParameterMap = propertyNameToTypeParameterMap;
+        this.propertyNameToTypeParameterMap = Collections.unmodifiableMap(propertyNameToTypeParameterMap);
         this.instanceCreatorFactory = instanceCreatorFactory;
         this.discriminatorEnabled = discriminatorEnabled;
         this.discriminatorKey = discriminatorKey;
         this.discriminator = discriminator;
         this.idPropertyModelHolder = idPropertyModelHolder;
-        this.propertyModels = propertyModels;
+        this.propertyModels = Collections.unmodifiableList(propertyModels);
     }
 
     /**