[DataFrame] Null Reference on ElementwiseEquals on DateTime columns from DataFrame

[novelhawk]

System Information (please complete the following information):

• OS & Version: [e.g. Windows 10] Windows 10
• ML.NET Version: [e.g. ML.NET v1.5.5] N/A
• Microsoft.Data.Analysis Version: 0.20.1
• .NET Version: [e.g. .NET 5.0]: 7.0.110

Describe the bug Invoking ElementwiseEquals on a PrimitiveDataFrameColumn obtained by accessing DataFrame["ColumnName"] throws NullReferenceException

To Reproduce

1. Create a PrimitiveDataFrameColumn with some values
2. Create a dataframe with the column using its constructor
3. Access the dataframe's column by using the this[string column] getter, es: df["ColumnName"]
4. Call the ElementwiseEquals method on the column obtained through the DataFrame
5. Observe that a NullReferenceException is thrown.
6. Call the same method on the column passed to the DataFrame constructor.
7. Observe that no exceptions are thrown

Expected behavior df["Test"] should behave like column and should not throw exceptions.

Screenshots, Code, Sample Projects Reproduction example:

#r "nuget: Microsoft.Data.Analysis, 0.20.1"
using Microsoft.Data.Analysis;

var column = new DateTimeDataFrameColumn("Test");
column.Append(DateTime.Today);
var df = new DataFrame(column);
Console.WriteLine(column == df["Test"]); // true
Console.WriteLine(column.ElementwiseEquals(DateTime.Today).Any()); // True
df["Test"].ElementwiseEquals(DateTime.Today) // Throws NullReferenceException

Stack trace Error: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.Data.Analysis.PrimitiveDataFrameColumn1.ElementwiseEqualsImplementation[U](U value) at Microsoft.Data.Analysis.PrimitiveDataFrameColumn1.ElementwiseEquals[U](U value) at Submission#6.<>d__0.MoveNext() --- End of stack trace from previous location --- at Microsoft.CodeAnalysis.Scripting.ScriptExecutionState.RunSubmissionsAsync[TResult](ImmutableArray1 precedingExecutors, Func2 currentExecutor, StrongBox1 exceptionHolderOpt, Func2 catchExceptionOpt, CancellationToken cancellationToken)