Please get checker-qual and error_prone_annotations to agree with caffeine...update your check-qual dependency to 2.6.0 and your error_prone_annotations dependency to 2.3.3, please.

    Require upper bound dependencies error for org.checkerframework:checker-qua>
        +-com.google.guava:guava:27.1-jre (managed) <-- com.google.guava:guava:>
          +-org.checkerframework:checker-qual:2.5.2
    and
        +-com.github.ben-manes.caffeine:caffeine:2.7.0
          +-org.checkerframework:checker-qual:2.6.0

    Require upper bound dependencies error for com.google.errorprone:error_pron>
        +-com.google.guava:guava:27.1-jre (managed) <-- com.google.guava:guava:>
          +-com.google.errorprone:error_prone_annotations:2.2.0
    and
        +-com.github.ben-manes.caffeine:caffeine:2.7.0
          +-com.google.errorprone:error_prone_annotations:2.3.3

public void testGet_primitives() {
    assertNull(ArbitraryInstances.get(void.class));
    assertNull(ArbitraryInstances.get(Void.class));
    assertEquals(Boolean.FALSE, ArbitraryInstances.get(boolean.class));
    assertEquals(Boolean.FALSE, ArbitraryInstances.get(Boolean.class));
    assertEquals(Character.valueOf('\0'), ArbitraryInstances.get(char.class));
    assertEquals(Character.valueOf('\0'), ArbitraryInstances.get(Character.class));
    assertEquals(Byte.valueOf((byte) 0), ArbitraryInstances.get(byte.class));
    assertEquals(Byte.valueOf((byte) 0), ArbitraryInstances.get(Byte.class));
    assertEquals(Short.valueOf((short) 0), ArbitraryInstances.get(short.class));
    assertEquals(Short.valueOf((short) 0), ArbitraryInstances.get(Short.class));
    assertEquals(Integer.valueOf(0), ArbitraryInstances.get(int.class));
    assertEquals(Integer.valueOf(0), ArbitraryInstances.get(Integer.class));
    assertEquals(Long.valueOf(0), ArbitraryInstances.get(long.class));
    assertEquals(Long.valueOf(0), ArbitraryInstances.get(Long.class));
    assertEquals(Float.valueOf(0), ArbitraryInstances.get(float.class));
    assertEquals(Float.valueOf(0), ArbitraryInstances.get(Float.class));
    assertEquals(Double.valueOf(0), ArbitraryInstances.get(double.class));
    assertEquals(Double.valueOf(0), ArbitraryInstances.get(Double.class));
    assertEquals(UnsignedInteger.ZERO, ArbitraryInstances.get(UnsignedInteger.class));
    assertEquals(UnsignedLong.ZERO, ArbitraryInstances.get(UnsignedLong.class));
    assertEquals(0, ArbitraryInstances.get(BigDecimal.class).intValue());
    assertEquals(0, ArbitraryInstances.get(BigInteger.class).intValue());
    assertEquals("", ArbitraryInstances.get(String.class));
    assertEquals("", ArbitraryInstances.get(CharSequence.class));
    assertEquals(TimeUnit.SECONDS, ArbitraryInstances.get(TimeUnit.class));
    assertNotNull(ArbitraryInstances.get(Object.class));