"cache lookup failed for type 0" when COPYing into existing cstore about cstore_fdw HOT 4 CLOSED

diff --git a/cstore_writer.c b/cstore_writer.c
index 052c6fa..4057429 100644
--- a/cstore_writer.c
+++ b/cstore_writer.c
@@ -148,9 +148,16 @@ CStoreBeginWrite(const char *filename, CompressionType compressionType,
    comparisonFunctionArray = palloc0(columnCount * sizeof(FmgrInfo *));
    for (columnIndex = 0; columnIndex < columnCount; columnIndex++)
    {
-       Oid typeId = tupleDescriptor->attrs[columnIndex]->atttypid;
-       FmgrInfo *comparisonFunction = GetFunctionInfoOrNull(typeId, BTREE_AM_OID,
-                                                            BTORDER_PROC);
+       FmgrInfo *comparisonFunction = NULL;
+
+       bool columnDropped = tupleDescriptor->attrs[columnIndex]->attisdropped;
+       if (!columnDropped)
+       {
+           Oid typeId = tupleDescriptor->attrs[columnIndex]->atttypid;
+           comparisonFunction = GetFunctionInfoOrNull(typeId, BTREE_AM_OID,
+                                                      BTORDER_PROC);
+       }
+
        comparisonFunctionArray[columnIndex] = comparisonFunction;
    }