1.7.7版本报空指针异常NullPointerException

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2021-03-26 18:58:05.857 20493-23439/ W/System.err: java.lang.NullPointerException: Attempt to invoke interface method 'com.liulishuo.filedownloader.model.FileDownloadModel com.liulishuo.filedownloader.database.FileDownloadDatabase.find(int)' on a null object reference
2021-03-26 18:58:05.857 20493-23439/ W/System.err: at android.os.Parcel.readException(Parcel.java:1690)
2021-03-26 18:58:05.857 20493-23439/ W/System.err: at android.os.Parcel.readException(Parcel.java:1637)
2021-03-26 18:58:05.857 20493-23439/ W/System.err: at com.liulishuo.filedownloader.i.IFileDownloadIPCService$Stub$Proxy.start(IFileDownloadIPCService.java:301)
2021-03-26 18:58:05.857 20493-23439/ W/System.err: at com.liulishuo.filedownloader.FileDownloadServiceUIGuard.start(FileDownloadServiceUIGuard.java:106)
2021-03-26 18:58:05.857 20493-23439/ W/System.err: at com.liulishuo.filedownloader.FileDownloadServiceProxy.start(FileDownloadServiceProxy.java:68)
2021-03-26 18:58:05.857 20493-23439/ W/System.err: at com.liulishuo.filedownloader.DownloadTaskHunter.start(DownloadTaskHunter.java:607)
2021-03-26 18:58:05.857 20493-23439/ W/System.err: at com.liulishuo.filedownloader.FileDownloadTaskLauncher$LaunchTaskRunnable.run(FileDownloadTaskLauncher.java:155)
2021-03-26 18:58:05.857 20493-23439/ W/System.err: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
2021-03-26 18:58:05.858 20493-23439/ W/System.err: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
2021-03-26 18:58:05.858 20493-23439/ W/System.err: at java.lang.Thread.run(Thread.java:761)
2021-03-26 18:58:05.858 20493-23444/ W/System.err: java.lang.NullPointerException: Attempt to invoke interface method 'com.liulishuo.filedownloader.model.FileDownloadModel com.liulishuo.filedownloader.database.FileDownloadDatabase.find(int)' on a null object reference
2021-03-26 18:58:05.858 20493-23444/ W/System.err: at android.os.Parcel.readException(Parcel.java:1690)
2021-03-26 18:58:05.859 20493-23444/ W/System.err: at android.os.Parcel.readException(Parcel.java:1637)
2021-03-26 18:58:05.859 20493-23444/ W/System.err: at com.liulishuo.filedownloader.i.IFileDownloadIPCService$Stub$Proxy.start(IFileDownloadIPCService.java:301)
2021-03-26 18:58:05.859 20493-23444/ W/System.err: at com.liulishuo.filedownloader.FileDownloadServiceUIGuard.start(FileDownloadServiceUIGuard.java:106)
2021-03-26 18:58:05.859 20493-23444/ W/System.err: at com.liulishuo.filedownloader.FileDownloadServiceProxy.start(FileDownloadServiceProxy.java:68)
2021-03-26 18:58:05.859 20493-23444/ W/System.err: at com.liulishuo.filedownloader.DownloadTaskHunter.start(DownloadTaskHunter.java:607)
2021-03-26 18:58:05.859 20493-23444/d W/System.err: at com.liulishuo.filedownloader.FileDownloadTaskLauncher$LaunchTaskRunnable.run(FileDownloadTaskLauncher.java:155)
2021-03-26 18:58:05.859 20493-23444/ W/System.err: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
2021-03-26 18:58:05.859 20493-23444/ W/System.err: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
2021-03-26 18:58:05.859 20493-23444/ W/System.err: at java.lang.Thread.run(Thread.java:761)
2021-03-26 18:58:05.860 20493-23439/ W/System.err: java.lang.NullPointerException: Attempt to invoke interface method 'com.liulishuo.filedownloader.model.FileDownloadModel com.liulishuo.filedownloader.database.FileDownloadDatabase.find(int)' on a null object reference
2021-03-26 18:58:05.860 20493-23439/ W/System.err: at android.os.Parcel.readException(Parcel.java:1690)
2021-03-26 18:58:05.861 20493-23439/ W/System.err: at android.os.Parcel.readException(Parcel.java:1637)
2021-03-26 18:58:05.861 20493-23439/ W/System.err: at com.liulishuo.filedownloader.i.IFileDownloadIPCService$Stub$Proxy.start(IFileDownloadIPCService.java:301)
2021-03-26 18:58:05.861 20493-23439/ W/System.err: at com.liulishuo.filedownloader.FileDownloadServiceUIGuard.start(FileDownloadServiceUIGuard.java:106)
2021-03-26 18:58:05.861 20493-23439/ W/System.err: at com.liulishuo.filedownloader.FileDownloadServiceProxy.start(FileDownloadServiceProxy.java:68)

Start with the start path in FileDownloadServiceUIGuard.java, FileDownloadServiceProxy.java, and DownloadTaskHunter.java, then trace the IPC call to FileDownloadDatabase.find. Reproduce the NullPointerException on version 1.7.7 and determine why the database reference is null; done means the start path no longer produces this exception and the behavior is verified.

Written by the indexing model from the issue text.