Fraction must have unit denominator when studying Elliptic Curve over complex field? [closed]

edit

I have the following elliptic curves defined over $\mathbb{C}$ depending on a parameter $a \in \mathbb{C}$:

$$ E_1: y^2 + xy = x^3 + ax + a $$ $$ E_2: y^2 + xy = x^3 + \frac{1}{a}x + \frac{1}{a} $$

That translated to code should look like this:

QQbar_a = QQbar['a']
QQbar_a.inject_variables()

E1 = EllipticCurve(QQbar_a, [1, 0, 0, a, a])
print(E1)

E2 = EllipticCurve(QQbar_a, [1, 0, 0, 1/a, 1/a])
print(E2)

While defining $E_1$ works fine, defining $E_2$ returns the following error:

TypeError: fraction must have unit denominator

I do not understand if the problem is that I have not specified that $a \neq 0$ (if so, how can I specify it?) or something else. Do you have any guess?