ValueError: can not merge DataFrame with instance of type 
#### Code Sample, a copy-pastable example if possible

```python
df_debtor = pd.merge(debtor_marital,debtor_gender, left_on = "IDENTITY", right_on = "IDENTITY", how = "inner")

```
#### Problem description
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
 in 
----> 1 df_debtor = pd.merge(debtor_marital,debtor_gender, left_on = "IDENTITY", right_on = "IDENTITY", how = "inner")

~/opt/anaconda3/lib/python3.7/site-packages/modin/pandas/general.py in merge(left, right, how, on, left_on, right_on, left_index, right_index, sort, suffixes, copy, indicator, validate)
     75     if not isinstance(left, DataFrame):
     76         raise ValueError(
---> 77             "can not merge DataFrame with instance of type {}".format(type(right))
     78         )
     79 

### ValueError: can not merge DataFrame with instance of type 
