diff --git a/src/somef/process_repository.py b/src/somef/process_repository.py
index 4c304af6..2258e008 100644
--- a/src/somef/process_repository.py
+++ b/src/somef/process_repository.py
@@ -774,10 +774,17 @@ def download_github_files(directory, owner, repo_name, repo_ref, authorization):
     with open(repo_zip_file, "wb") as f:
         f.write(repo_zip)
 
-    with zipfile.ZipFile(repo_zip_file, "r") as zip_ref:
-        zip_ref.extractall(repo_extract_dir)
-
+    try:
+        with zipfile.ZipFile(repo_zip_file, "r") as zip_ref: 
+            zip_ref.extractall(repo_extract_dir) 
+    except zipfile.BadZipFile: 
+        logging.error("Downloaded archive is not a valid zip (repo may be empty)") 
+        return None
+    
     repo_folders = os.listdir(repo_extract_dir)
+    if not repo_folders: 
+        logging.warning("Repository archive is empty") 
+        return None
 
     repo_dir = os.path.join(repo_extract_dir, repo_folders[0])
     return repo_dir
diff --git a/src/somef/test/test_JSON_export.py b/src/somef/test/test_JSON_export.py
index f92368a3..33ad9aa7 100644
--- a/src/somef/test/test_JSON_export.py
+++ b/src/somef/test/test_JSON_export.py
@@ -427,7 +427,7 @@ def test_issue_830(self):
     #     data = text_file.read()
     #     text_file.close()
     #     json_content = json.loads(data)
- 
+
     #     assert "description" in json_content, "Missing 'description' property" 
    
     #     assert len(json_content["description"]) > 0, "Description list is empty" 
@@ -438,5 +438,37 @@ def test_issue_830(self):
         
     #     os.remove(test_data_path + "test_issue_862.json")
 
+    def test_issue_859(self):
+        """Checks whether a repository without content works fine. Must have just some results from the API."""
+
+        somef_cli.run_cli(threshold=0.8,
+                        ignore_classifiers=False,
+                        repo_url="https://github.com/shiningZZ/GU-CAFF",
+                        local_repo=None,
+                        doc_src=None,
+                        in_file=None,
+                        output=test_data_path + "test-859.json",
+                        graph_out=None,
+                        graph_format="turtle",
+                        codemeta_out= None,
+                        pretty=True,
+                        missing=False,
+                        readme_only=False)
+        
+        with open(test_data_path + "test-859.json", "r") as text_file: 
+            json_content = json.load(text_file)
+
+        assert "code_repository" in json_content 
+        assert len(json_content["code_repository"]) > 0
+        
+        for key, entries in json_content.items(): 
+            if isinstance(entries, list): 
+                for entry in entries: 
+                    assert entry.get("technique") == "GitHub_API", \
+                    f"Unexpected technique {entry.get('technique')} in key {key}"
+
+        os.remove(test_data_path + "test-859.json")
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/src/somef/utils/constants.py b/src/somef/utils/constants.py
index ea084231..1775da1a 100644
--- a/src/somef/utils/constants.py
+++ b/src/somef/utils/constants.py
@@ -24,7 +24,9 @@
 REGEXP_PYPI_2 = "[![Latest PyPI version]"
 REGEXP_COLAB = "https://colab.research.google.com/drive"
 # needed to cleanup bibtext files.
-REGEXP_BIBTEX = r'\@[a-zA-Z]+\{[.\n\S\s]+?[author|title][.\n\S\s]+?[author|title][.\n\S\s]+?\n\}'
+# REGEXP_BIBTEX = r'\@[a-zA-Z]+\{[.\n\S\s]+?[author|title][.\n\S\s]+?[author|title][.\n\S\s]+?\n\}'
+# REGEXP_BIBTEX = r'@[a-zA-Z]+\{[\s\S]*?(?:author|title)[\s\S]*?(?:author|title)[\s\S]*?\}'
+REGEXP_BIBTEX = r'@[a-zA-Z]+\{(?=[\s\S]*\bauthor\b)(?=[\s\S]*\btitle\b)[\s\S]*?\}'
 REGEXP_DOI = r'\[\!\[DOI\]([^\]]+)\]\(([^)]+)\)'
 REGEXP_LINKS = r"\[(.*?)?\]\(([^)]+)\)"
 REGEXP_IMAGES = r"!\[(.*?)?\]\((.*?)?\)"