Runtime VerifyError: Verifier rejected class with Android <= 21

[willpowr]

Occurs when executing test line:
List<DateGroup> groups = parser.parse("the day before next thursday");

Test is in AndroidTest

Conditions of error...
Type: runtime
Target: Android Studio emulator or device
Gradle config: minSdkVersion 21 or lower

java.lang.VerifyError: Verifier rejected class com.joestelmach.natty.generated.DateParser_NumericRules: com.joestelmach.natty.generated.DateParser_NumericRules$spelled_first_to_thirty_first_return com.joestelmach.natty.generated.DateParser_NumericRules.spelled_first_to_thirty_first() failed to verify: com.joestelmach.natty.generated.DateParser_NumericRules$spelled_first_to_thirty_first_return com.joestelmach.natty.generated.DateParser_NumericRules.spelled_first_to_thirty_first(): [0xC94] copy1 v5<-v314 type=Undefined cat=1 (declaration of 'com.joestelmach.natty.generated.DateParser_NumericRules' appears in /data/app/com.willpoweru.nattybaretest-DPlh2Z16fzvqmVZgf0mVYA==/base.apk)
at com.joestelmach.natty.generated.DateParser.(DateParser.java:470)
at com.joestelmach.natty.Parser.singleParse(Parser.java:200)
at com.joestelmach.natty.Parser.parse(Parser.java:100)
at com.joestelmach.natty.Parser.parse(Parser.java:67)
at com.willpoweru.nattybaretest.ExampleInstrumentedTest.nattyTest(ExampleInstrumentedTest.java:36)
at java.lang.reflect.Method.invoke(Native Method)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at android.support.test.runner.AndroidJUnit4.run(AndroidJUnit4.java:101)
at org.junit.runners.Suite.runChild(Suite.java:128)
at org.junit.runners.Suite.runChild(Suite.java:27)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
at android.support.test.internal.runner.TestExecutor.execute(TestExecutor.java:56)
at android.support.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:384)
at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:2075)