Occasional Pager NullPointerException from recurly-java-client

[gstanek]

Describe the bug

We see occasional NullPointerExceptions propagated out of the recurly-client-java. The relevant observed stack trace is:

java.util.concurrent.ExecutionException: java.lang.NullPointerException: Cannot invoke "com.recurly.v3.Pager.getNext()" because "pager" is null
	at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
	at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
	at com.sproutsocial.revenue.internal.account.v1.service.AccountServiceImpl.getAccountResponse(AccountServiceImpl.java:872)
	at com.sproutsocial.revenue.internal.account.v1.service.AccountServiceImpl.getAccountsBatches(AccountServiceImpl.java:281)
	at com.sproutsocial.revenue.internal.account.v1.service.AccountServiceImpl.lambda$getAccounts$0(AccountServiceImpl.java:239)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at com.sproutsocial.revenue.commons.multithreading.MdcThreadPoolExecutor$1.run(MdcThreadPoolExecutor.java:99)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:840)
	Caused by: java.lang.NullPointerException: Cannot invoke "com.recurly.v3.Pager.getNext()" because "pager" is null
	at com.recurly.v3.Pager.clone(Pager.java:93)
	at com.recurly.v3.Pager.getNextPage(Pager.java:89)
	at com.sproutsocial.revenue.internal.client.RecurlyClientImpl.executePaginatedQueryInEnv(RecurlyClientImpl.java:740)
	at com.sproutsocial.revenue.internal.client.RecurlyClientImpl.getPaginatedEntitiesById(RecurlyClientImpl.java:685)
	at com.sproutsocial.revenue.internal.client.RecurlyClientImpl.listInvoicesByAccountCode(RecurlyClientImpl.java:536)
	at com.sproutsocial.revenue.internal.account.v1.service.AccountServiceImpl.lambda$getAccountResponse$6(AccountServiceImpl.java:835)
	... 5 common frames omitted

Specifically of note:

	Caused by: java.lang.NullPointerException: Cannot invoke "com.recurly.v3.Pager.getNext()" because "pager" is null
	at com.recurly.v3.Pager.clone(Pager.java:93)
	at com.recurly.v3.Pager.getNextPage(Pager.java:89)

Our theory is some sort of network exception prevents this.client.makeRequest from returning an instantiated pager object, leading to the NullPointerException within the clone method.

To Reproduce

This does not happen consistently or often (the rate has been a few times a month). Given the stack trace, this bug appears to be entirely within the context of the recurly-client-java code.

Expected behavior

The recurly java client does not encounter NullPointerExceptions, causing failed transactions.

Your Environment

• Which version of this library are you using?

    <dependency>
      <groupId>com.recurly.v3</groupId>
      <artifactId>api-client</artifactId>
      <version>4.51.0</version>
      <exclusions>
        <exclusion>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
        </exclusion>
      </exclusions>
    </dependency>

• Which version of the language are you using?
  Java 17