Evaluation dies for 0-row view

[bgribaudo]

Preflight Checklist

• I have installed the latest version of Power Query SDK.
• I have checked existing resources, including the common issues and the release notes.
• I have searched for similar issues.

Power Query SDK

0.2.1

Regression From

No response

Platform

Windows

Architecture

x64

OS Version

No response

VSCode version

No response

PQSdkTool Path

No response

Bug Description

When data is requested from a connector that returns a view which outputs a zero-row table, evaluation dies with an exception.

Steps to Reproduce

1. Create a connector defined as follows:

   section Test;
   
   [DataSource.Kind="Test"]
   shared Test.Contents = () =>
       Table.View(null, [
           GetRows = () => #table({"A"}, {{}}),
           GetType = () => Value.Type(GetRows())
       ]);
   
   Test = [ Authentication = [ Anonymous = [] ] ];
   

2. Evaluate the following test script: Test.Contents()

Actual Experience

Evaluate dies with the following error:

"Error": {
            "Message": "1 keys were specified, but 0 values were provided.",
            "MessageFormat": "{0} keys were specified, but {1} values were provided.",
            "MessageParameters": [
                "1",
                "0"
            ],
            "Details": {
                "Reason": "Expression.Error",
                "Detail": "{error \"Microsoft.Mashup.Engine1.Runtime.ValueException: [Expression.Error] Value was not specified.#(cr)#(lf)   at Microsoft.Mashup.Engine1.Language.ValueCreator.CreateValueForNotImplemented(INotImplementedExpression expression)#(cr)#(lf)   at Microsoft.Mashup.Engine1.Runtime.ListValue.DemandArrayListValue.get_Item(Int32 index)#(cr)#(lf)   at Microsoft.Data.Mashup.ProviderCommon.MashupResource.TryGetValue(Func`1 getValue, IValue& value, String& errorMessage)#(cr)#(lf)Record\"}"
            }
        }

Expected Experience

A 0-row table should be successfully returned.

Additional Context

If the Table.View code is copied out of the connector and placed into the .test.pq file, then that file is evaluated, the expected table is returned without error.

[mattmasson]

It looks like this is an engine bug / quirk of Table.View, rather than an issue with the SDK itself. The GetRows handler does not like the empty list value in the table row.

This works:

#table({"A"}, {})

But this throws an exception:

#table({"A"}, {{}}

I've opened a tracking bug internally.

[bgribaudo]

Thank you, @mattmasson!