diff --git a/.github/workflows/pythonpackage.yml b/.github/workflows/pythonpackage.yml
new file mode 100644
index 0000000..407d0eb
--- /dev/null
+++ b/.github/workflows/pythonpackage.yml
@@ -0,0 +1,39 @@
+# This workflow will install Python dependencies, run tests and lint with a variety of Python versions
+# For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions
+
+name: Python package
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [3.5, 3.6, 3.7, 3.8]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v1
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install flake8 pytest
+        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+    - name: Lint with flake8
+      run: |
+        # stop the build if there are Python syntax errors or undefined names
+        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+        # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
+        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+    - name: Test with pytest
+      run: |
+        tox
diff --git a/AUTHORS b/AUTHORS
index 2b5edc7..07c6bce 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -1,8 +1,10 @@
 Ahmed Tahri
 akeonly
+Alexander Bougakov
 Alex Debiasio
 Asuki Kono
 belono
+Brian
 Christoph Heuel
 Cody (Quantified Code Bot)
 csoft2k
@@ -19,6 +21,7 @@ Kristi
 ldos
 Lucy Linder
 Manuel F Martinez
+Maximilian Wagenbach
 Michael Billington
 Michael Elsdörfer
 mrwunderbar666
diff --git a/README.rst b/README.rst
index 1cf2e6c..fd7e83b 100644
--- a/README.rst
+++ b/README.rst
@@ -76,6 +76,25 @@ Another example based on the Network printer class:
     kitchen.text("Hello World\n")
     kitchen.barcode('1324354657687', 'EAN13', 64, 2, '', '')
     kitchen.cut()
+    
+Another example based on the Serial printer class:
+
+.. code:: python
+
+    from escpos.printer import Serial
+    
+    """ 9600 Baud, 8N1, Flow Control Enabled """
+    p = Serial(devfile='/dev/tty.usbserial',
+               baudrate=9600,
+               bytesize=8,
+               parity='N',
+               stopbits=1,
+               timeout=1.00,
+               dsrdtr=True)
+
+    p.text("Hello World\n")
+    p.qr("You can readme from your smartphone")
+    p.cut()
 
 
 The full project-documentation is available on `Read the Docs <https://python-escpos.readthedocs.io>`_.
diff --git a/src/escpos/escpos.py b/src/escpos/escpos.py
index d22ffd0..17e0d12 100644
--- a/src/escpos/escpos.py
+++ b/src/escpos/escpos.py
@@ -102,6 +102,9 @@ class Escpos(object):
             * `graphics`: prints with the `GS ( L`-command
             * `bitImageColumn`: prints with the `ESC *`-command
 
+        When trying to center an image make sure you have initialized the printer with a valid profile, that
+        contains a media width pixel field. Otherwise the centering will have no effect.
+
         :param img_source: PIL image or filename to load: `jpg`, `gif`, `png` or `bmp`
         :param high_density_vertical: print in high density in vertical direction *default:* True
         :param high_density_horizontal: print in high density in horizontal direction *default:* True
@@ -113,6 +116,10 @@ class Escpos(object):
         im = EscposImage(img_source)
 
         try:
+            if self.profile.profile_data['media']['width']['pixels'] == "Unknown":
+                print("The media.width.pixel field of the printer profile is not set. " +
+                      "The center flag will have no effect.")
+
             max_width = int(self.profile.profile_data['media']['width']['pixels'])
 
             if im.width > max_width: