issue in saveString method

[zeeldev01]

    at java.io.FileDescriptor.sync(FileDescriptor.java)
   at android.os.FileUtils.sync(FileUtils.java:245)
   at android.app.SharedPreferencesImpl.writeToFile(SharedPreferencesImpl.java:807)
   at android.app.SharedPreferencesImpl.access$900(SharedPreferencesImpl.java:59)
   at android.app.SharedPreferencesImpl$2.run(SharedPreferencesImpl.java:672)
   at android.app.SharedPreferencesImpl.enqueueDiskWrite(SharedPreferencesImpl.java:691)
   at android.app.SharedPreferencesImpl.access$100(SharedPreferencesImpl.java:59)
   at android.app.SharedPreferencesImpl$EditorImpl.commit(SharedPreferencesImpl.java:604)
   at com.anjlab.android.iab.v3.BillingBase.saveString(BillingBase.java)
   at com.anjlab.android.iab.v3.BillingProcessor.savePurchasePayload(BillingProcessor.java)
   at com.anjlab.android.iab.v3.BillingProcessor.purchase(BillingProcessor.java)
   at com.anjlab.android.iab.v3.BillingProcessor.subscribe(BillingProcessor.java)
   at com.pdfreaderviewer.pdfmaker.pdfeditor.activity.PremiumActivity.getSubscribe(PremiumActivity.java)
   at com.pdfreaderviewer.pdfmaker.pdfeditor.activity.PremiumActivity.onClick(PremiumActivity.java)