Index out of range Error for ScriptDefinition '$a=1' on pwsh 6.1.0.-preview.1 only

Steps to reproduce

Invoke-scriptanalyzer -script '$a=1'

Expected behavior

Triggers PSUseDeclaredVarsMoreThanAssignments rule.

Actual behavior

RuleName                            Severity     ScriptName Line  Message
--------                            --------     ---------- ----  -------
out-lineoutput : Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
+ CategoryInfo          : NotSpecified: (:) [out-lineoutput], ArgumentOutOfRangeException
+ FullyQualifiedErrorId : System.ArgumentOutOfRangeException,Microsoft.PowerShell.Commands.OutLineOutputCommand

Environment data

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      6.1.0-preview.1
PSEdition                      Core
GitCommitId                    v6.1.0-preview.1
OS                             Linux 4.13.0-38-generic #43~16.04.1-Ubuntu SMP Wed Mar 14 17:48:43 UTC 2018
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

> (Get-Module -ListAvailable PSScriptAnalyzer).Version | ForEach-Object { $_.ToString() }
1.16.1

Start by reproducing the reported command, Invoke-ScriptAnalyzer -Script '$a=1', with PowerShell 6.1.0-preview.1 and PSScriptAnalyzer 1.16.1. Trace the ScriptDefinition handling and output path that produces the index error; done means the command completes and reports PSUseDeclaredVarsMoreThanAssignments without an out-of-range exception.