Ramban, on Gen 38:7

“And Her, the firstborn of Juda, was wicked in the sight of the Lord: and was slain by him.”

“AND ER, JUDAH’s FIRSTBORN, WAS WICKED IN THE SIGHT OF THE ETERNAL. Scripture does not specify the nature of his wickedness as it did in the case of his brother. Instead, it simply states that he died for his own sin. It informs us that this was not by way of punishment of Judah for his role in the sale of Joseph, since the saving of Joseph’s life by Judah compensated for his role in the sale. There was no case of death of a child in the house of the patriarchs except this one who was wicked in the sight of the Eternal, since the race of the righteous is blessed. This is why Jacob mourned many days for his son Joseph, and he refused to comfort himself, for he considered this to be a great punishment to himself, quite apart from his love for him.”

Imported from an open dataset — not yet checked against the printed edition.