SqlAG: Throws exception when BasicAvailabilityGroup is set to $false

Details of the scenario you tried and the problem that is occurring:
When configuring an Availability Group on SQL Server 2017 and the configuration contains the parameter BasicAvailabilityGroup and set to $false it throws an error.

This is probably due to that it doesn't compare the BasicAvailabilityGroup value correctly if we look at the verbose output.

2017-11-04_13-26-24: 'BasicAvailabilityGroup' should be 'False' but is ''

Full output below.

ERBOSE: [SQLTEST]: LCM:  [ Start  Resource ]  [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1]
VERBOSE: [SQLTEST]: LCM:  [ Start  Test     ]  [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1]
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Information: PowerShell module SqlServer not found, trying to use older SQLPS module.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Importing PowerShell module SQLPS.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Connected to SQL instance 'sqltest\SQL2017'.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] 2017-11-04_13-26-24: 'BasicAvailabilityGroup' should be 'False' but is ''
VERBOSE: [SQLTEST]: LCM:  [ End    Test     ]  [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1]  in 0.8910 seconds.
VERBOSE: [SQLTEST]: LCM:  [ Start  Set      ]  [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1]
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Information: PowerShell module SqlServer not found, trying to use older SQLPS module.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Importing PowerShell module SQLPS.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Information: PowerShell module SqlServer not found, trying to use older SQLPS module.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Importing PowerShell module SQLPS.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Connected to SQL instance 'sqltest\SQL2017'.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Getting the effective permissions for the login 'NT SERVICE\ClusSvc' on 'SQL2017'.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Information: PowerShell module SqlServer not found, trying to use older SQLPS module.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Importing PowerShell module SQLPS.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] Connected to SQL instance 'SQLTEST\SQL2017'.
VERBOSE: [SQLTEST]:                            [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1] The cluster login 'NT SERVICE\ClusSvc' has the required permissions.
VERBOSE: [SQLTEST]: LCM:  [ End    Set      ]  [[xSQLServerAlwaysOnAvailabilityGroup]SQL2017-TESTCLU02-AddAvailabilityGroupTESTCLU02-AG1]  in 1.3120 seconds.
PowerShell DSC resource MSFT_xSQLServerAlwaysOnAvailabilityGroup  failed to execute Set-TargetResource functionality with error message: Failed to alter the availability group 'TESTCLU02-AG1'. InnerException: Exception calling "Alter" w
ith "0" argument(s): "Alter failed for Availability Group 'TESTCLU02-AG1'. "
    + CategoryInfo          : InvalidOperation: (:) [], CimException
    + FullyQualifiedErrorId : ProviderOperationExecutionFailure
    + PSComputerName        : sqltest.shamn.se

A workaround is simply to remove BasicAvailabilityGroup = $false from the configuration. But I think the resource should handle this.

The DSC configuration that is using the resource (as detailed as possible):

                xSQLServerAlwaysOnAvailabilityGroup $resourceConfigName
                {
                    Ensure = 'Present'
                    Name = $Node.AvailabilityGroupName
                    SQLInstanceName = $Node."$($currentSqlInstance)InstanceName"
                    SQLServer = $Node.NodeName
                    BasicAvailabilityGroup = $false

                    PsDscRunAsCredential = $SqlAdministratorCredential

                    DependsOn = "[xSQLServerEndpoint]$($currentSqlInstance)-HADREndpoint",
                                "[xSQLServerPermission]$($currentSqlInstance)-AddNTServiceClusSvcPermissions"
                }

Version of the Operating System, SQL Server and PowerShell the DSC Target Node is running:
Windows Server 2012 R2, SQL Server 2017

What module (SqlServer or SQLPS) and which version of the module the DSC Target Node is running:
SQLPS

Version of the DSC module you're using, or 'dev' if you're using current dev branch:
Dev

Start by locating the xSQLServerAlwaysOnAvailabilityGroup resource and its handling of the BasicAvailabilityGroup parameter, then reproduce the configuration against SQL Server 2017 using the SQLPS module. Done means BasicAvailabilityGroup = $false is compared and applied correctly without reporting an empty value or failing the availability group alteration.