diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index dd1e3ceb0d98..16bb91733581 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -32,7 +32,9 @@ bndlib = { module = "biz.aQute.bnd:biz.aQute.bndlib", version.ref = "bnd" }
 checkstyle = { module = "com.puppycrawl.tools:checkstyle", version.ref = "checkstyle" }
 classgraph = { module = "io.github.classgraph:classgraph", version = "4.8.181" }
 commons-io = { module = "commons-io:commons-io", version = "2.20.0" }
-errorProne-core = { module = "com.google.errorprone:error_prone_core", version = "2.42.0" }
+error-prone-core = { module = "com.google.errorprone:error_prone_core", version = "2.42.0" }
+error-prone-contrib = { module = "tech.picnic.error-prone-support:error-prone-contrib", version = "0.25.0" }
+refaster-runner = { module = "tech.picnic.error-prone-support:refaster-runner", version = "0.25.0" }
 fastcsv = { module = "de.siegmar:fastcsv", version = "4.0.0" }
 groovy = { module = "org.apache.groovy:groovy", version = "5.0.1" }
 groovy2-bom = { module = "org.codehaus.groovy:groovy-bom", version = "2.5.23" }
diff --git a/gradle/plugins/common/src/main/kotlin/junitbuild.java-nullability-conventions.gradle.kts b/gradle/plugins/common/src/main/kotlin/junitbuild.java-nullability-conventions.gradle.kts
index 2bef782b14ed..568cc6cd7048 100644
--- a/gradle/plugins/common/src/main/kotlin/junitbuild.java-nullability-conventions.gradle.kts
+++ b/gradle/plugins/common/src/main/kotlin/junitbuild.java-nullability-conventions.gradle.kts
@@ -1,6 +1,7 @@
 import junitbuild.extensions.dependencyFromLibs
 import net.ltgt.gradle.errorprone.errorprone
 import net.ltgt.gradle.nullaway.nullaway
+import org.gradle.jvm.toolchain.JvmImplementation.J9
 
 plugins {
 	`java-library`
@@ -9,61 +10,80 @@ plugins {
 }
 
 dependencies {
-	errorprone(dependencyFromLibs("errorProne-core"))
+	errorprone(dependencyFromLibs("error-prone-contrib"))
+	errorprone(dependencyFromLibs("error-prone-core"))
 	errorprone(dependencyFromLibs("nullaway"))
+	errorprone(dependencyFromLibs("refaster-runner"))
 	constraints {
 		errorprone("com.google.guava:guava") {
 			version {
 				require("33.4.8-jre")
 			}
 			because("Older versions use deprecated methods in sun.misc.Unsafe")
+			// https://github.com/junit-team/junit-framework/pull/5039#discussion_r2414490581
 		}
 	}
 }
 
-nullaway {
-	onlyNullMarked = true
-}
-
 tasks.withType<JavaCompile>().configureEach {
 	options.errorprone {
-		val shouldDisableErrorProne = java.toolchain.implementation.orNull == JvmImplementation.J9
-		if (name == "compileJava" && !shouldDisableErrorProne) {
+//		allErrorsAsWarnings = true
+//		disableAllWarnings = true
+		disableAllChecks = !(J9 != java.toolchain.implementation.orNull && "compileJava" == name)
+		if (!disableAllChecks.get()) {
+			// errorproneArgs.add("-XepOpt:Refaster:NamePattern=^(?!.*Rules\\$).*") // currently failing Refaster; might consider whitelist.
 			disable(
-
-				// This check is opinionated wrt. which method names it considers unsuitable for import which includes
-				// a few of our own methods in `ReflectionUtils` etc.
-				"BadImport",
-
-				// The findings of this check are subjective because a named constant can be more readable in many cases
-				"UnnecessaryLambda",
-
-				// Resolving findings for these checks requires ErrorProne's annotations which we don't want to use
-				"AnnotateFormatMethod",
+				"AnnotateFormatMethod", // We don`t want to use ErrorProne`s annotations.
+				"BadImport", // This check is opinionated wrt. which method names it considers unsuitable for import which includes a few of our own methods in `ReflectionUtils` etc.
 				"DoNotCallSuggester",
-				"InlineMeSuggester",
 				"ImmutableEnumChecker",
+				"InlineMeSuggester",
+				"MissingSummary", // Produces a lot of findings that we consider to be false positives, for example for package-private classes and methods.
+				"StringSplitter", // We don`t want to use Guava.
+				"UnnecessaryLambda", // The findings of this check are subjective because a named constant can be more readable in many cases.
+				// picnic (https://error-prone.picnic.tech)
+				"ConstantNaming",
+				"DirectReturn", // https://github.com/junit-team/junit-framework/pull/5006#discussion_r2403984446
+				"FormatStringConcatenation",
+				"IdentityConversion",
+				"LexicographicalAnnotationAttributeListing",
+				"LexicographicalAnnotationListing",
+				"UnnecessarilyFullyQualified",
+				"MissingTestCall",
+				"NestedOptionals",
+				"StaticImport",
+				"NonStaticImport",
+				"CanIgnoreReturnValueSuggester",
+				"OptionalOrElseGet",
+				"ThrowsUncheckedException",
+				"TimeZoneUsage",
+			)
+			error(
+				"PackageLocation",
+				"RedundantStringConversion",
+				"RedundantStringEscape",
+			)
+			// introduce new check by activating once:
+			// CompositeFilter.java:75: Note: [Refaster Rule] OptionalRules.OptionalOrElseThrow: Refactoring opportunity
 
-				// Resolving findings for this check requires using Guava which we don't want to use
-				"StringSplitter",
-
-				// Produces a lot of findings that we consider to be false positives, for example for package-private
-				// classes and methods
-				"MissingSummary",
+			errorproneArgs.addAll(
+				"-Xep:Refaster:ERROR", // TODO  why failing not on warning error prone stuff? https://errorprone.info/bugpattern/AvoidObjectArrays
+				"-XepOpt:Refaster:NamePattern=OptionalRules", // without this it's going cray-cray, having to disable all failing checks.
+//				"-XepPatchChecks:OptionalRules",
+				"-XepPatchLocation:IN_PLACE",
+				"-XepOpt:Refaster:NamePattern=OptionalRules.OptionalOrElseThrow"
 			)
-			error("PackageLocation")
-		} else {
-			disableAllChecks = true
 		}
 		nullaway {
-			if (shouldDisableErrorProne) {
-				disable()
-			} else {
+			if (J9 == java.toolchain.implementation.orNull) {
 				enable()
+			} else {
+				disable()
 			}
-			isJSpecifyMode = true
-			customContractAnnotations.add("org.junit.platform.commons.annotation.Contract")
 			checkContracts = true
+			customContractAnnotations.add("org.junit.platform.commons.annotation.Contract")
+			isJSpecifyMode = true
+			onlyNullMarked = true
 			suppressionNameAliases.add("DataFlowIssue")
 		}
 	}
diff --git a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/PreInterruptThreadDumpPrinter.java b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/PreInterruptThreadDumpPrinter.java
index 283710eb1f1e..94147129d87b 100644
--- a/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/PreInterruptThreadDumpPrinter.java
+++ b/junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/PreInterruptThreadDumpPrinter.java
@@ -49,7 +49,7 @@ public void beforeThreadInterrupt(PreInterruptContext preInterruptContext, Exten
 					sb.append(NL);
 					// Use the same prefix as java.lang.Throwable.printStackTrace(PrintStreamOrWriter)
 					sb.append("\tat ");
-					sb.append(stackTraceElement.toString());
+					sb.append(stackTraceElement);
 				}
 				sb.append(NL);
 			}