Exception in documentation example of `maxByOrNull`

In [Operations/Access/Get Rows](https://kotlin.github.io/dataframe/getrow.html) we have:

```
df.maxByOrNull { weight }
```

Executing this in a Kotlin Notebook cell results in: `Type mismatch: inferred type is Int? but Int was expected`

Gradle settings:

```
plugins {
kotlin("jvm") version "2.2.20-Beta1"
kotlin("plugin.dataframe") version "2.2.20-Beta1"
}

dependencies {
implementation("org.jetbrains.kotlinx:dataframe:1.0.0-Beta2")
testImplementation(kotlin("test"))
}
```

Open the Operations/Access/Get Rows page linked in the issue and reproduce the maxByOrNull example in a Kotlin Notebook using the provided Gradle settings. Update the documentation example so it executes without the reported type mismatch, then rerun the example to verify it.

Written by the indexing model from the issue text.