amended mkdocs missing message to allign with sphinx

Author: silentfatez

readthedocs/doc_builder/backends/mkdocs.py

@@ -12,6 +12,7 @@
 
 from readthedocs.core.utils.filesystem import safe_open
 from readthedocs.doc_builder.base import BaseBuilder
+from readthedocs.doc_builder.exceptions import MkDocsYAMLParseError
 from readthedocs.projects.constants import MKDOCS, MKDOCS_HTML
 
 log = structlog.get_logger(__name__)
@@ -80,6 +81,12 @@ def get_yaml_config(self):
     def show_conf(self):
         """Show the current ``mkdocs.yaml`` being used."""
         # Write the mkdocs.yml to the build logs
+        if not os.path.exists(self.yaml_file):
+            raise MkDocsYAMLParseError(
+                message_id=MkDocsYAMLParseError.NOT_FOUND,
+
+            )
+        
         self.run(
             "cat",
             os.path.relpath(self.yaml_file, self.project_path),