PostgreSQL SMALLINT[] mapping fails in Dapper 2.1.86 but works in 2.1.79

PostgreSQL SMALLINT[] mapping fails in Dapper 2.1.86 but works in Dapper 2.1.79.

Environment

• .NET 10
• PostgreSQL
• Npgsql
• Dapper 2.1.86

Database

CREATE TABLE auto_numbers
(
    item_name TEXT NOT NULL,
    auto_column_name TEXT NOT NULL,
    separator_positions SMALLINT[] NOT NULL DEFAULT ARRAY[]::SMALLINT[],
    PRIMARY KEY (item_name, auto_column_name)
);

Example value:

INSERT INTO auto_numbers
    (item_name, auto_column_name, separator_positions)
VALUES
    ('queue_visits', 'token_no', ARRAY[1]::SMALLINT[]);

Model

public sealed record AutoNumberRequest
{
    public required string ItemName { get; init; }
    public required string AutoColumnName { get; init; }
    public required IReadOnlyList<short> SeparatorPositions { get; init; } = [];
}

Query

const string sql = """
    SELECT
        item_name "ItemName",
        auto_column_name "AutoColumnName",
        separator_positions "SeparatorPositions"
    FROM auto_numbers
    WHERE item_name = @ItemName
      AND auto_column_name = @AutoColumnName
    """;

var result = await connection.QuerySingleAsync<AutoNumberRequest>(
    sql,
    new
    {
        ItemName = "queue_visits",
        AutoColumnName = "token_no"
    });

Error with Dapper 2.1.86

System.Data.DataException:
Error parsing column 2 (SeparatorPositions=System.Int16[] - Int16[])

System.InvalidCastException:
Object must implement IConvertible.

   at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
   ...

Npgsql returns the PostgreSQL SMALLINT[] value as System.Int16[].

Version comparison

With Dapper 2.1.79:

<PackageReference Include="Dapper" Version="[2.1.79]" />

the same query and model work correctly.

With Dapper 2.1.86:

<PackageReference Include="Dapper" Version="[2.1.86]" />

the query fails with the exception above.

I also tested changing the property from:

IReadOnlyList<short>

to:

short[]

and short[] also fails with Dapper 2.1.86.

No other application or database changes were made between the tests.

This appears to be a regression in Dapper 2.1.86 when reading PostgreSQL SMALLINT[] values through Npgsql.

Dapper 2.1.79 continues to work correctly with the same PostgreSQL database, Npgsql setup, query, and model.

Start by reproducing the SMALLINT[] query with Npgsql and Dapper 2.1.86 using the AutoNumberRequest model and QuerySingleAsync call shown in the issue, then compare it with 2.1.79. Trace the column-mapping path for the System.Int16[] value; done means the query maps SeparatorPositions successfully without the IConvertible exception.