Error: uncaught exception.

[THREAD]
main
[EXCEPTION]
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.algobase.hrv_monitor/com.algobase.hrv.HRV_Activity}: androidx.fragment.app.w: Unable to instantiate fragment x.a: could not find Fragment constructor
Unable to start activity ComponentInfo{com.algobase.hrv_monitor/com.algobase.hrv.HRV_Activity}: androidx.fragment.app.w: Unable to instantiate fragment x.a: could not find Fragment constructor

[STACK TRACE]
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.algobase.hrv_monitor/com.algobase.hrv.HRV_Activity}: androidx.fragment.app.w: Unable to instantiate fragment x.a: could not find Fragment constructor
	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4169)
	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4325)
	at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:101)
	at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
	at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2574)
	at android.os.Handler.dispatchMessage(Handler.java:106)
	at android.os.Looper.loopOnce(Looper.java:226)
	at android.os.Looper.loop(Looper.java:313)
	at android.app.ActivityThread.main(ActivityThread.java:8757)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:571)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)
Caused by: androidx.fragment.app.w: Unable to instantiate fragment x.a: could not find Fragment constructor
	at androidx.fragment.app.n0.a(SourceFile:71)
	at androidx.fragment.app.y0.<init>(SourceFile:12)
	at androidx.fragment.app.t0.w0(SourceFile:112)
	at androidx.fragment.app.f0.w(SourceFile:8)
	at androidx.fragment.app.a0.a(SourceFile:29)
	at c.a.c(SourceFile:20)
	at androidx.activity.ComponentActivity.onCreate(SourceFile:7)
	at androidx.fragment.app.FragmentActivity.onCreate(SourceFile:0)
	at com.algobase.hrv.HRV_Activity.onCreate(SourceFile:9)
	at android.app.Activity.performCreate(Activity.java:8591)
	at android.app.Activity.performCreate(Activity.java:8570)
	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1384)
	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4150)
	... 12 more
Caused by: java.lang.NoSuchMethodException: x.a.<init> []
	at java.lang.Class.getConstructor0(Class.java:2363)
	at java.lang.Class.getConstructor(Class.java:1759)
	at androidx.fragment.app.n0.a(SourceFile:36)
	... 24 more

android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4169)
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4325)
android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:101)
android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
android.app.ActivityThread$H.handleMessage(ActivityThread.java:2574)
android.os.Handler.dispatchMessage(Handler.java:106)
android.os.Looper.loopOnce(Looper.java:226)
android.os.Looper.loop(Looper.java:313)
android.app.ActivityThread.main(ActivityThread.java:8757)
java.lang.reflect.Method.invoke(Native Method)
com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:571)
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)