title: Send password reset email method crashes the app
body: <p>I am trying to make a forget password activity where there is an EditText field for user to input their e-mail and click a Button and the sendPasswordResetEmail() method will be invoked... So the code that I have is this</p>
  <pre><code>mAuth = FirebaseAuth.getInstance();
  resetPasswordBtn = (Button)findViewById(R.id.resetPasswordButton);
  resetPasswordFld = (EditText)findViewById(R.id.resetPasswordField);
  
  final String email = resetPasswordFld.getText().toString().trim();
  
  resetPasswordBtn.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View view) {
          mAuth.sendPasswordResetEmail(email)
                  .addOnCompleteListener(new OnCompleteListener&lt;Void&gt;() {
                      @Override
                      public void onComplete(@NonNull Task&lt;Void&gt; task) {
                          if (task.isSuccessful()) {
                              Toast.makeText(ResetPassword.this, &quot;e-mail buat reset password sudah dikirimkan&quot;,Toast.LENGTH_LONG).show();
                              Intent loginIntent = new Intent (ResetPassword.this, LoginActivity.class);
                              startActivity(loginIntent);
                          }
                      }
                  });
      }
  });
  </code></pre>
  <p>When I tried it, the app crashes, and I got this error log</p>
  <pre><code>03-23 16:28:59.829 6990-6990E/UncaughtException: java.lang.IllegalArgumentException: Given String is empty or null
      at com.google.android.gms.common.internal.zzac.zzdv(Unknown Source)
      at com.google.firebase.auth.FirebaseAuth.sendPasswordResetEmail(Unknown Source)
      at com.ResetPassword$1.onClick(ResetPassword.java:37)
      at android.view.View.performClick(View.java:6207)
      at android.widget.TextView.performClick(TextView.java:11094)
      at android.view.View$PerformClick.run(View.java:23639)
      at android.os.Handler.handleCallback(Handler.java:751)
      at android.os.Handler.dispatchMessage(Handler.java:95)
      at android.os.Looper.loop(Looper.java:154)
      at android.app.ActivityThread.main(ActivityThread.java:6688)
      at java.lang.reflect.Method.invoke(Native Method)
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
  03-23 16:28:59.833 6990-7024 D/FA: Logging event (FE): _ae, Bundle[{_o=crash, _sc=ResetPassword, _si=-8440426569227389093, timestamp=1490261339829, fatal=1}]
  03-23 16:29:00.128 6990-6990 E/AndroidRuntime: FATAL EXCEPTION: main
   Process: , PID: 6990
   java.lang.IllegalArgumentException: Given String is empty or null
   at com.google.android.gms.common.internal.zzac.zzdv(Unknown Source)
   at com.google.firebase.auth.FirebaseAuth.sendPasswordResetEmail(Unknown Source)
   at.ResetPassword$1.onClick(ResetPassword.java:37)
   at android.view.View.performClick(View.java:6207)
   at android.widget.TextView.performClick(TextView.java:11094)
   at android.view.View$PerformClick.run(View.java:23639)
   at android.os.Handler.handleCallback(Handler.java:751)
   at android.os.Handler.dispatchMessage(Handler.java:95)
   at android.os.Looper.loop(Looper.java:154)
   at android.app.ActivityThread.main(ActivityThread.java:6688)
   at java.lang.reflect.Method.invoke(Native Method)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
  </code></pre>
  <p>I am actually convinced that I am doing this wrong as mAuth will definitely returns null as no user is logged in right? I am having difficulties finding good documentation about this and the documentation in the firebase documentations does not really help.</p>
  <p>There must be a way to reference a database to check if the email address inputted really exists... But my rules prevent users that aren't logged in to access them... So I am just really confused on how to get started with this...</p>