Default value for the null column?

How can we handle the null value for the data mapping process? I'm getting the encoding exception if the value of the column coming back from SQL database is NULL.

org.springframework.core.codec.EncodingException: JSON encoding error: (was java.lang.NullPointerException); nested exception is com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: java.util.ArrayList[0]->com.sun.proxy.$Proxy96["sales_dollars"])
at org.springframework.http.codec.json.AbstractJackson2Encoder.encodeValue(AbstractJackson2Encoder.java:135) ~[spring-web-5.0.0.RELEASE.jar:5.0.0.RELEASE]
at org.springframework.http.codec.json.AbstractJackson2Encoder.lambda$encode$3(AbstractJackson2Encoder.java:108) ~[spring-web-5.0.0.RELEASE.jar:5.0.0.RELEASE]
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:107) ~[reactor-core-3.1.0.RELEASE.jar:3.1.0.RELEASE]
at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1085) ~[reactor-core-3.1.0.RELEASE.jar:3.1.0.RELEASE]
at reactor.core.publisher.MonoCollectList$MonoBufferAllSubscriber.onComplete(MonoCollectList.java:117) ~[reactor-core-3.1.0.RELEASE.jar:3.1.0.RELEASE]
at io.reactivex.internal.util.HalfSerializer.onComplete(HalfSerializer.java:91) ~[rxjava-2.1.7.jar:na]
at io.reactivex.internal.subscribers.StrictSubscriber.onComplete(StrictSubscriber.java:109) ~[rxjava-2.1.7.jar:na]
at io.reactivex.internal.operators.flowable.FlowableFlatMap$MergeSubscriber.drainLoop(FlowableFlatMap.java:426) ~[rxjava-2.1.7.jar:na]
at io.reactivex.internal.operators.flowable.FlowableFlatMap$MergeSubscriber.drain(FlowableFlatMap.java:366) ~[rxjava-2.1.7.jar:na]
at io.reactivex.internal.operators.flowable.FlowableFlatMap$MergeSubscriber.onComplete(FlowableFlatMap.java:338) ~[rxjava-2.1.7.jar:na]
at io.reactivex.internal.subscriptions.DeferredScalarSubscription.complete(DeferredScalarSubscription.java:135) ~[rxjava-2.1.7.jar:na]
at io.reactivex.internal.operators.single.SingleToFlowable$SingleToFlowableObserver.onSuccess(SingleToFlowable.java:63) ~[rxjava-2.1.7.jar:na]
at io.reactivex.internal.operators.single.SingleMap$MapSingleObserver.onSuccess(SingleMap.java:64) ~[rxjava-2.1.7.jar:na]
at org.davidmoten.rx.pool.MemberSingle$Emitter.run(MemberSingle.java:528) ~[rxjava2-jdbc-0.1-RC23.jar:na]
at io.reactivex.internal.schedulers.ExecutorScheduler$ExecutorWorker$BooleanRunnable.run(ExecutorScheduler.java:260) ~[rxjava-2.1.7.jar:na]
at io.reactivex.internal.schedulers.ExecutorScheduler$ExecutorWorker.run(ExecutorScheduler.java:225) ~[rxjava-2.1.7.jar:na]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) ~[na:1.8.0_131]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) ~[na:1.8.0_131]
at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_131]
Caused by: com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: java.util.ArrayList[0]->com.sun.proxy.$Proxy96["sales_dollars"])
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:391) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:351) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:316) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:727) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:145) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:107) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:25) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:400) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1392) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ObjectWriter._configAndWriteValue(ObjectWriter.java:1120) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:950) ~[jackson-databind-2.9.1.jar:2.9.1]
at org.springframework.http.codec.json.AbstractJackson2Encoder.encodeValue(AbstractJackson2Encoder.java:129) ~[spring-web-5.0.0.RELEASE.jar:5.0.0.RELEASE]
... 18 common frames omitted
Caused by: java.lang.NullPointerException: null
at com.sun.proxy.$Proxy96.sales_dollars(Unknown Source) ~[na:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_131]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_131]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_131]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_131]
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:687) ~[jackson-databind-2.9.1.jar:2.9.1]
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719) ~[jackson-databind-2.9.1.jar:2.9.1]
... 28 common frames omitted