Server Error in `/` Application.

Server Error in '/' Application.
Conversion from type 'DBNull' to type 'String' is not valid.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and
where it originated in the code.
Exception Details: System.InvalidCastException: Conversion from type 'DBNull' to type 'String' is not valid.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information
regarding the origin and location of the exception can be identified using the exception stack trace
below.
Stack Trace:
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This documentation is not intended as a substitute for and is not to be used for determining suitability or reliability of these products for specific user applications.
It is the duty of any such user or integrator to perform the appropriate and complete risk analysis, evaluation and testing of the products with respect to the relevant specific application or use thereof.
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[InvalidCastException: Conversion from type 'DBNull' to type 'String' is not valid.]
Microsoft.VisualBasic.CompilerServices.Conversions.ToString(Object Value) +1073
eRef.PdfGenerator.Web.partnumber_eShop_v3.PartnumberTechnicalInfo(Int32 _SalesOrgId, String _ProductId, Int32 _LanguageCode) +5
eRef.PdfGenerator.Web.partnumber_eShop_v3.Page_Load(Object sender, EventArgs e) +1699
System.Web.UI.Control.LoadRecursive() +116
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2750
Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.1031
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