Understanding the significance of an exclamation point preceding a period

Recently, I came across this code snippet:

fixture.componentInstance.dataSource!.data = [];

I am intrigued by the syntax dataSource!.data and would like to understand its significance.

While familiar with using a question mark (?) before a dot (.) as in key1?.key2, the exclamation point (!) preceding the dot (.) in the expression !. has piqued my interest.

Any insights or explanations would be greatly appreciated!

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