Connector Rule - Object reference not set to an instance of an object

When I use that function, I get the following error:

Those are declared as constants

#Region "Constants and Enumerations"

		Dim connectionName As String = "OneStream BI Blend"		
		
		Dim columnNames As String() = {"Account", "AccountType", "Amount", "Credit", "Debit", "Department", "Entity", "Flow", "IC", "Location", "PLCategory", "SourceID", "UD1_ProfitCentre", "UD2_Category", "UD3_Projects", "UD4_DataAudit"}
		
		Dim columnNamesDrillBack As String() = {"Entity", "EntityDesc", "Period", "Account", "AccountDesc", "AccountType", "Debit", "Credit", "Amount", "Debit", "Credit", "Amount", "PLCategory", "Division", "Department", "DepartmentDesc", "Location", "LocationDesc", "PropertyLocation", "PropertyLocationDesc", "ProjectCode", "ProjectCodeDesc"}
		
		Dim accountTypePL As String() = {"COGS", "DeferExpense", "Expense", "Income", "OthExpense", "OthIncome"}
		Dim accountTypeBS As String() = {"AcctPay", "AcctRec", "Bank", "Equity", "FixedAsset", "OthAsset", "OthCurrAsset", "OthCurrLiab", "NonPosting"}
	
		Dim accountTypeSignFlip As String() = {"Income", "OthIncome", "AcctPay", "Equity", "OthCurrLiab"}
		
#End Region