diff --git a/library/src/main/api21/com/google/android/cameraview/Camera2.java b/library/src/main/api21/com/google/android/cameraview/Camera2.java
index 4835f89e..e21fdfce 100644
--- a/library/src/main/api21/com/google/android/cameraview/Camera2.java
+++ b/library/src/main/api21/com/google/android/cameraview/Camera2.java
@@ -132,6 +132,9 @@ public void onClosed(@NonNull CameraCaptureSession session) {
 
         @Override
         public void onPrecaptureRequired() {
+            if (mPreviewRequestBuilder == null || mCaptureSession == null) {
+                return;
+            }
             mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER,
                     CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START);
             setState(STATE_PRECAPTURE);
@@ -580,6 +583,10 @@ void updateFlash() {
      * Locks the focus as the first step for a still image capture.
      */
     private void lockFocus() {
+        if (mPreviewRequestBuilder == null || mCaptureCallback == null || mCaptureSession == null) {
+            return;
+        }
+
         mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER,
                 CaptureRequest.CONTROL_AF_TRIGGER_START);
         try {
@@ -635,16 +642,18 @@ void captureStillPicture() {
                             mDisplayOrientation * (mFacing == Constants.FACING_FRONT ? 1 : -1) +
                             360) % 360);
             // Stop preview and capture a still picture.
-            mCaptureSession.stopRepeating();
-            mCaptureSession.capture(captureRequestBuilder.build(),
-                    new CameraCaptureSession.CaptureCallback() {
-                        @Override
-                        public void onCaptureCompleted(@NonNull CameraCaptureSession session,
-                                @NonNull CaptureRequest request,
-                                @NonNull TotalCaptureResult result) {
-                            unlockFocus();
-                        }
-                    }, null);
+            if (mCaptureSession != null) {
+                mCaptureSession.stopRepeating();
+                mCaptureSession.capture(captureRequestBuilder.build(),
+                        new CameraCaptureSession.CaptureCallback() {
+                            @Override
+                            public void onCaptureCompleted(@NonNull CameraCaptureSession session,
+                                    @NonNull CaptureRequest request,
+                                    @NonNull TotalCaptureResult result) {
+                                unlockFocus();
+                            }
+                        }, null);
+            }
         } catch (CameraAccessException e) {
             Log.e(TAG, "Cannot capture a still picture.", e);
         }
@@ -655,6 +664,10 @@ public void onCaptureCompleted(@NonNull CameraCaptureSession session,
      * capturing a still picture.
      */
     void unlockFocus() {
+        if (mPreviewRequestBuilder == null || mCaptureCallback == null || mCaptureSession == null) {
+            return;
+        }
+
         mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER,
                 CaptureRequest.CONTROL_AF_TRIGGER_CANCEL);
         try {