Properly handle cases when path to a file with a defect is unknown

Resolves #4237

HISTORY.rst

@@ -54,6 +54,7 @@ Please check `Migration guide from 5.x to 6.0 <https://docs.platformio.org/en/la
 
   - Added support for the custom `Clang-Tidy <https://docs.platformio.org/en/latest/plus/check-tools/clang-tidy.html>`__ configuration file (`issue #4186 <https://github.com/platformio/platformio-core/issues/4186>`_)
   - Added ability to override a tool version using the `platform_packages <https://docs.platformio.org/en/latest/projectconf/section_env_platform.html#platform-packages>`__ option (`issue #3798 <https://github.com/platformio/platformio-core/issues/3798>`_)
+  - Fixed an issue with improper handling of defects that don't specify a source file (`issue #4237 <https://github.com/platformio/platformio-core/issues/4237>`_)
 
 * **Build System**
 

platformio/commands/check/defect.py

@@ -34,7 +34,7 @@ class DefectItem(object):
         severity,
         category,
         message,
-        file="unknown",
+        file=None,
         line=0,
         column=0,
         id=None,
@@ -50,7 +50,7 @@ class DefectItem(object):
         self.callstack = callstack
         self.cwe = cwe
         self.id = id
-        self.file = file
+        self.file = file or "unknown"
         if file.lower().startswith(get_project_dir().lower()):
             self.file = os.path.relpath(file, get_project_dir())