Why does a single function running in SQL Server CLR cause a stand-alone application to crash?

The two methods below are similar, except that one processes null values ​​and the other does not. To handle null values, it uses the SqlString type and checks the get_IsNull property.

Why can the first cause an error "A .NET Framework error occurred during execution of user-defined routine or aggregate "CheckMailingAddress": ."when running inside the SQL CLR, and the second can not?

In particular, the TSQL error "Msg 10329, Level 16, State 49, Line 1 .Net Framework execution was aborted."

.method public hidebysig static bool CheckMailingAddress(valuetype [System.Data]System.Data.SqlTypes.SqlString param0) cil managed
{
   .maxstack 8
    L_0000: ldarga.s param0
    L_0002: nop 
    L_0003: nop 
    L_0004: call instance bool [System.Data]System.Data.SqlTypes.SqlString::get_IsNull()
    L_0009: brfalse L_0010
    L_000e: ldc.i4.1 
    L_000f: ret 
    L_0010: ldarga.s param0
    L_0012: nop 
    L_0013: nop 
    L_0014: call instance string [System.Data]System.Data.SqlTypes.SqlString::get_Value()
    L_0019: call class DatabaseValues.MailingAddress DatabaseValues.MailingAddress::op_Explicit(string)
    L_001e: pop 
    L_001f: ldc.i4.1 
    L_0020: ret 
}

.method public hidebysig static bool CheckMailingAddress(string param0) cil managed
{
   .maxstack 8
    L_0000: ldarg.0 
    L_0001: call class DatabaseValues.CheckMailingAddress DatabaseValues.CheckMailingAddress::op_Explicit(string)
    L_0006: pop 
    L_0007: ldc.i4.1 
    L_0008: ret 
}

Keep in mind that MSIL is correct, as far as I know, because both of these methods work when called in a standalone application. It is only when called inside the SQL CLR that the first of two crashes. In the SQL CLR, a function is defined with the type "nvarchar (4000)", which, as far as I know, should work well with SqlString.

, , , "string", , SqlString, INULable "IsNull" "Value", , Sql *.

:

, MSIL ; . , , , "SqlString", "string", , CLR , NULL, TRUE.

//Crashes when input parameter is "SqlString"
.method public hidebysig static bool CheckMailingAddress(valuetype [System.Data]System.Data.SqlTypes.SqlString param0) cil managed
{
   .maxstack 8
    L_001f: ldc.i4.1 
    L_0020: ret 
}

//Doesn't Crash when input parameter is "string"
.method public hidebysig static bool CheckMailingAddress(string param0) cil managed
{
   .maxstack 8 
    L_0007: ldc.i4.1 
    L_0008: ret 
}