Running checker on an Android library project fails with Gradle 6.4.1, passes with Gradle 6.2.2

When I build my project with gradle 6.4.1, it fails with:

FAILURE: Build failed with an exception.

* Where:
Build file '/Users/hborders/workspace/sqldim/sqldim/build.gradle' line: 84

* What went wrong:
org.codehaus.groovy.runtime.GStringImpl cannot be cast to java.lang.String

line 84 is:

options.forkOptions.jvmArgs += ["-Xbootclasspath/p:${configurations.errorproneJavac.asPath}"]

https://github.com/typetools/checker-framework/issues/1916 has a workaround, which also fixed my problem:

options.forkOptions.jvmArgs += ["-Xbootclasspath/p:${configurations.errorproneJavac.asPath}".toString()]

For an easy fix, please update the guide to include this workaround. For a proper fix, please make the workaround unnecessary.

My project is available for testing: https://github.com/hborders/sqldim/tree/checker_3339

Start with the Gradle configuration at line 84 of the reported build.gradle and compare behavior under Gradle 6.4.1 and 6.2.2. Review the linked Checker Framework issue and the Android project at the checker_3339 branch. Done means the guide documents the workaround and, if feasible, the build succeeds without it.