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POMap NullPointerException in Play Framework
 

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    <p>I have a class for Vehicle and what I'm trying to do is link a bunch of VehicleParts to this Vehicle. Obviously, a normal vehicle can't have two engines, so what I'm thinking of storing them in is a map, more specifically an EnumMap</p> <pre><code>public enum VehiclePartType { ENGINE_BLOCK, CRANKSHAFT, //..etc } public class VehiclePart { public String name; public VehiclePartType partType; //some more basic variables + ModelFinder } public class Vehicle { //some basic string variables and a ModelFinder @ManyToMany public Map&lt;VehiclePartType, VehiclePart&gt; parts = new EnumMap&lt;VehiclePartType, VehiclePart&gt;(VehiclePartType.class); } </code></pre> <p>Usage: When i try to associate a part with a given vehicle.</p> <pre><code>Vehicle vehicle = Vehicle.finderVehicle.byId(id); VehiclePart vehiclePart = VehiclePart.finderVehiclePart.byId(partId); vehicle.parts.put(VehiclePartType.ENGINE_BLOCK, vehiclePart); vehicle.saveManyToManyAssociations("parts"); </code></pre> <p>This creates the table I want in the SQL database and stores the proper reference IDs, but whenever I try to access it via Java code, such as the following code, I get an error:</p> <pre><code>Vehicle.allVehicles(); [RuntimeException: java.lang.IllegalArgumentException: (was java.lang.NullPointerException) (through reference chain: com.avaje.ebean.common.BeanList[1]-&gt;models.Vehicle["parts"])] </code></pre> <p>If I change the map to a list, this works fine, but that's not what I'm going for since I won't be able to get a part by its VehiclePartType without searching through the entire list of parts.</p> <p>First, is this an acceptable way of storing the VehicleParts?<br> Second, I'm not sure how to resolve this null error. Any help with this would be appreciated.</p>
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