serena init/config load crashes when generated config has empty projects key

[ShivamB25]

I have:

• read the relevant parts of the documentation and verified that the issue cannot be solved by adjusting configuration
• understood that the Serena Dashboard can be disabled through the config
• understood that, by default, a client session will start a separate instance of a Serena server.
• understood that, for multi-agent setups, the Streamable HTTP/SSE mode should be used.
• understood that non-project files are ignored using either .gitignore or the corresponding setting in .serena/project.yml
• looked for similar issues and discussions, including closed ones
• made sure it's an actual issue, not a question (use GitHub Discussions instead).

If you have encountered an actual issue:

• If using language servers (not the JetBrains plugin),
  • I performed <uv invocation> serena project health-check (not applicable: this fails during init/config loading before project setup)
  • I indexed the project as described in the documentation (not applicable: this fails during init/config loading before project setup)
• I added sufficient explanation of my setup: the MCP client, the OS, the programming language(s), any config adjustments or relevant project specifics
• I explained how the issue arose and, where possible, added instructions on how to reproduce it
• If the issue happens on an open-source project, I have added the link (not project-specific)
• I provided a meaningful title and description

Summary

SerenaConfig.from_config_file() crashes when serena_config.yml contains an empty projects: key. The generated config in my environment ended with projects: (no list entries), which YAML loads as None; the config loader then tries to iterate it.

Steps to reproduce

Install and initialize Serena:

uv tool install -p 3.13 serena-agent@latest --prerelease=allow
serena init

In the generated/current config, the final section is:

# the list of registered project paths (updated automatically).
projects:

Then loading the config reproduces the crash:

/home/ubuntu/.local/share/uv/tools/serena-agent/bin/python - <<'PY'
from serena.config.serena_config import SerenaConfig
SerenaConfig.from_config_file()
PY

Actual result

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "/home/ubuntu/.local/share/uv/tools/serena-agent/lib/python3.13/site-packages/serena/config/serena_config.py", line 846, in from_config_file
    for path in loaded_commented_yaml["projects"]:
                ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^
TypeError: 'NoneType' object is not iterable

The same traceback was seen from serena init:

Serena version: 1.1.2
...
File ".../serena/cli.py", line 158, in init
  serena_config = SerenaConfig.from_config_file()
...
TypeError: 'NoneType' object is not iterable

Expected result

Either:

1. the generated template should use projects: [], or
2. from_config_file() should treat a null/empty projects: value as an empty list and continue.

A config generated by Serena should not cause config loading or serena init to crash.

Environment

• Serena package: serena-agent 1.1.2
• Install command: uv tool install -p 3.13 serena-agent@latest --prerelease=allow
• Serena tool Python: 3.13
• Host Python: Python 3.12.3
• OS: Ubuntu Linux on aarch64 (Linux 6.17.0-1010-oracle)
• MCP/client context: setting up Serena MCP for a CLI agent environment; no project-specific language server involved yet

Likely cause

serena/config/serena_config.py checks only that the projects key exists, then iterates it:

if "projects" not in loaded_commented_yaml:
    raise SerenaConfigError(...)
instance.projects = []
for path in loaded_commented_yaml["projects"]:
    ...

When YAML contains projects: with no value, loaded_commented_yaml["projects"] is None.

[opcode81]

Serena itself will never generate a projects key with an empty value.
If you want to empty the list of projects manually, you must not define

projects:

but an empty list, as follows:

projects: []

[opcode81]

Executing the sequence of commands you mentioned (installation, init) does not produce the error with no faulty serena_config.yml present in ~/.serena/.