Não é possível gerar diagrama ERD com código Python

O Python a seguir foi projetado para gerar um ERD usando o Visual Studio Code.

O gráfico é criado localmente com matplotlib. O código executa sem erros, no entanto, o diagrama ERD mostra em branco.

O código python é o seguinte:

import matplotlib.pyplot as plt

# Define the entities and their attributes for the ERD
entities = {
    "Customer": ["CustomerID (PK)", "CustomerName", "ContactInfo"],
    "CreditCardAccount": ["AccountID (PK)", "AccountStatus", "Balance", "CustomerID (FK)"],
    "CreditCard": ["CardID (PK)", "CardNumber", "ExpiryDate", "AccountID (FK)", "BrandID (FK)"],
    "CreditCardBrand": ["BrandID (PK)", "BrandName", "CardType"],
    "SecondaryCardHolder": ["SecondaryHolderID (PK)", "HolderName", "RelationToPrimary", "AccountID (FK)"],
    "PurchaseTransaction": ["TransactionID (PK)", "TransactionDate", "Amount", "CardID (FK)", "RetailerID (FK)"],
    "Retailer": ["RetailerID (PK)", "RetailerName", "Location"],
    "MonthlyStatement": ["StatementID (PK)", "StatementDate", "OutstandingBalance", "AccountID (FK)"],
    "CustomerServiceInteraction": ["InteractionID (PK)", "InteractionDate", "Notes", "CustomerID (FK)"],
}

# Relationships between entities
relationships = [
    ("Customer", "CreditCardAccount", "1:M"),
    ("CreditCardAccount", "CreditCard", "1:M"),
    ("CreditCard", "CreditCardBrand", "M:1"),
    ("CreditCardAccount", "SecondaryCardHolder", "1:M"),
    ("CreditCard", "PurchaseTransaction", "1:M"),
    ("PurchaseTransaction", "Retailer", "M:1"),
    ("CreditCardAccount", "MonthlyStatement", "1:M"),
    ("Customer", "CustomerServiceInteraction", "1:M"),
]

# Plotting the ERD
fig, ax = plt.subplots(figsize=(12, 8))

# Define positions for the entities
positions = {
    "Customer": (1, 5),
    "CreditCardAccount": (4, 5),
    "CreditCard": (7, 5),
    "CreditCardBrand": (10, 5),
    "SecondaryCardHolder": (4, 3),
    "PurchaseTransaction": (7, 3),
    "Retailer": (10, 3),
    "MonthlyStatement": (4, 1),
    "CustomerServiceInteraction": (1, 3),
}

# Draw entities as boxes
for entity, position in positions.items():
    plt.text(position[0], position[1], f"{entity}\n" + "\n".join(entities[entity]),
             ha='center', va='center', bbox=dict(facecolor='lightblue', edgecolor='black', boxstyle='round,pad=0.5'))

# Draw relationships as lines
for rel in relationships:
    start_pos = positions[rel[0]]
    end_pos = positions[rel[1]]
    ax.annotate("",
                xy=end_pos, xycoords='data',
                xytext=start_pos, textcoords='data',
                arrowprops=dict(arrowstyle="->", lw=1.5, color='black'),
                )
    # Add cardinality
    midpoint = ((start_pos[0] + end_pos[0]) / 2, (start_pos[1] + end_pos[1]) / 2)
    ax.text(midpoint[0], midpoint[1], rel[2], ha='center', va='center', fontsize=10)

# Hide axes
ax.set_axis_off()

# Show the ERD diagram
plt.title("Entity Relationship Diagram (ERD) for Credit Card Company", fontsize=16)
plt.show()

A saída é a seguinte:

Alguém pode me dizer por que o ERD não aparece?