What does this error mean and do I need to worry about it?

I'm building an insert statement based on the presence of values in several pulldown menus in the preceding page.

It looks like this:

$insert_statement="";
			$handle=fopen("$csv_name", "r");
			$counter=0;
			while ((!$row=fgetcsv($handle))== false) 
			{
			$counter++;
				if($counter>1) //omit the column headings
				{
				//here's where you need to craft your query
				$insert_statement = 'insert into '.$table_name.'(';
				for($i=0; $i<=$_POST['column_count']; $i++)
				{
					if (isset($_POST['select_name_'.$i.'']) && $_POST['select_name_'.$i.'']=="")
					{
					header("location:csv_upload_error.php");
					exit();
					}
					else
					{
						$insert_statement.=$_POST['select_name_'.$i.''];
						if($i<$_POST['column_count'])
						{
							$insert_statement.=',';
						}
						else
						{
							$insert_statement.=', session_id)';
						}
					}
				}
				$insert_statement.=' VALUES (';
				for($i=0; $i<=$_POST['column_count']; $i++)
					{
						$the_row[$i]=$mysqli->real_escape_string($row[$i]);
						$insert_statement .='\'';
						$insert_statement .=$_POST['column_'.$i.''];
						$insert_statement .='\'';
						if($i<$_POST['column_count'])
						{
							$insert_statement.=',';
						}
						else
						{
							$insert_statement .=', \'';
							$insert_statement .="$the_session_id";
							$insert_statement .='\'';
							$insert_statement .=')';
						}
					}
				//echo $insert_statement;	
				//$query=$mysqli->query($insert_statement);
				}
			}
		}
		return $insert_statement;

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The good news is that it works. I can print each individual insert statement and verify that it's sound. I can go to the database and see that the data has been correctly inserted.

But at the top of my page, I get this error: Warning: mysqli::query(): Empty query in C:\wamp\www\vbs\upload\csvClass.php on line 268

Line 268 is this guy right here: if(!$query=$mysqli->query($insert_statement))...

I can copy and paste the compiled insert statement into phpMyAdmin and it works fine. Data, everything - good to go. But I keep getting this error and I don't know why.

Any suggestions?