android中的异常返回null

Question

我使用以下代码验证登录。大多数时候它的工作正常。但问题是有时会抛出异常。维护日志文件以捕获错误。当我检查日志文件时，它有＆＃34; Err-CLS-Test - NULL＆＃34;。以下是我的代码。怎么解决这个问题？

                mloginBtn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                try {

                        final String userName = mEdtTxtUserName.getText()
                                .toString();
                        String pswd = mEdtTxtPswd.getText().toString();

                                String uName = config.getSalesPersonCode();
                                String uPswd = config.getPassword();

                                if (userName.equalsIgnoreCase(uName)
                                        && pswd.equalsIgnoreCase(uPswd)) {
                                    mDbHelper.getReadableDatabase();
                                    String companyNo = mDbHelper.getCompanyCodeByName(companyName);
                                    mDbHelper.closeDatabase();
                                    mSupporter.setUsrCode(userName);
                                    mSupporter.setCompanyNo(companyNo);
                                    mSupporter.simpleNavigateTo(MainMenu.class);

                                } else {
                                    showAlert(
                                            "Enter valid User code and password.",
                                            "Invalid", R.drawable.warning);
                                    mloginBtn.setEnabled(true);
                                }

                            } 

                } catch (Exception exe) {
                    mToastMsg.showToast(LoginActivity.this, exe.getMessage());
                    exe.printStackTrace();
                    String errorCode = "Err-CLS-Test";
                    LogFileCreator.appendLog(errorCode + " : "
                            + exe.getMessage());
                    mloginBtn.setEnabled(true);
                }
});
    }

下面是我的StackTrace

14:16:28 - java.lang.NullPointerException
    at com.visualqc.controller.LoginActivity$1.onClick(LoginActivity.java:176)
    at android.view.View.performClick(View.java:4222)
    at android.view.View$PerformClick.run(View.java:17337)
    at android.os.Handler.handleCallback(Handler.java:615)
    at android.os.Handler.dispatchMessage(Handler.java:92)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4895)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:994)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761)
    at dalvik.system.NativeStart.main(Native Method)
 : null