Source dependencies not working?

I’m trying to use source dependencies in my project, but script compilation fails with:

  Line 25: sourceControl {
           ^ Unresolved reference: sourceControl

My version:


------------------------------------------------------------
Gradle 6.4
------------------------------------------------------------

Build time:   2020-05-05 19:18:55 UTC
Revision:     42f7c3d0c3066b7b38bd0726760d4881e86fd19f

Kotlin:       1.3.71
Groovy:       2.5.10
Ant:          Apache Ant(TM) version 1.10.7 compiled on September 1 2019
JVM:          14.0.1 (Oracle Corporation 14.0.1+7)
OS:           Mac OS X 10.15.4 x86_64