[BUG]

**Describe the bug**
A clear and concise description of what the bug is.
try commend
attributions = MAM(random_df=True)
after that have mistake:
ValueError: can not merge DataFrame with instance of type
**To Reproduce**
Steps to reproduce the behavior:
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns

!pip install marketing_attribution_models
from marketing_attribution_models import MAM
attributions = MAM(random_df=True)
4. See error
~\Anaconda3\lib\site-packages\pandas\core\reshape\merge.py in __init__(self, left, right, how, on, left_on, right_on, axis, left_index, right_index, sort, suffixes, copy, indicator, validate)
525 if not isinstance(right, DataFrame):
526 raise ValueError('can not merge DataFrame with instance of '
--> 527 'type {right}'.format(right=type(right)))
528
529 if not is_bool(left_index):

ValueError: can not merge DataFrame with instance of type

**Expected behavior**
without mistake ion test data

**Screenshots**
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**Additional context**
Add any other context about the problem here.