c# - Comparing two identical MDB tables, except one has the first column removed -

so, working on internal tool @ work compares 2 mdb files , lists differences between two. however, when testing tool 2 similar mdb's except second has first column removed, exception thrown @ following line:

ncompareresult = ((icomparable)leftrows[nleftrows][nleftsortedcolumn])                    .compareto(rightrows[nrightrow][nrightsortedcolumn]); 

what should comparison equal considering trying compare non-null table cell cell doesn't exist?

if not specific or overlooked please feel free let me know in comments.