Bug: Empty keys from single-`#` lines cause blank entries in Frank!Doc output

#### Description

Frank!Doc intentionally parses commented-out properties and properties without values to include them in the documentation. For example:

- `#property.name` → is correctly parsed as a property named `property.name` with no default value or description.
- `## Description`
`#property` → is parsed as a property named `property` with the description: `Description`.

I think this behavior is **intended** and **not a bug**.

However, a line like:

```properties
#
```

results in a **property with an empty key and no description**, which causes a **blank row** to appear in the generated documentation table.

#### Example

Code reference:
[`AppConstants.properties#L489`](https://github.com/frankframework/frankframework/blob/317ea9ff54490e56c56b371a491177e5a0b2eb22/core/src/main/resources/AppConstants.properties#L489)

#### Screenshot


#### Expected Behavior

Lines that consist of only a single `#`, or whitespace-only comment lines, should be ignored by the parser and **not result in documented properties**.

#### Actual Behavior

They are currently parsed as properties with empty keys, resulting in blank entries.

#### Proposed Solution

- Update the parser to **skip lines** where the resulting key is empty after parsing.
- Optionally log a warning or ignore such entries entirely during documentation generation.