diff --git a/android/guava-testlib/src/com/google/common/collect/testing/Helpers.java b/android/guava-testlib/src/com/google/common/collect/testing/Helpers.java
index 24cb640427af..bfc1ae1eccac 100644
--- a/android/guava-testlib/src/com/google/common/collect/testing/Helpers.java
+++ b/android/guava-testlib/src/com/google/common/collect/testing/Helpers.java
@@ -127,7 +127,7 @@ public static void assertEqualInOrder(Iterable<?> expected, Iterable<?> actual)
     }
   }
 
-  public static void assertContentsInOrder(Iterable<?> actual, Object... expected) {
+  public static void assertContentsInOrder(Iterable<?> actual, @Nullable Object... expected) {
     assertEqualInOrder(asList(expected), actual);
   }
 
@@ -155,11 +155,11 @@ public static void assertEqualIgnoringOrder(Iterable<?> expected, Iterable<?> ac
     assertTrue("unexpected elements: " + act, act.isEmpty());
   }
 
-  public static void assertContentsAnyOrder(Iterable<?> actual, Object... expected) {
+  public static void assertContentsAnyOrder(Iterable<?> actual, @Nullable Object... expected) {
     assertEqualIgnoringOrder(asList(expected), actual);
   }
 
-  public static void assertContains(Iterable<?> actual, Object expected) {
+  public static void assertContains(Iterable<?> actual, @Nullable Object expected) {
     boolean contained = false;
     if (actual instanceof Collection) {
       contained = ((Collection<?>) actual).contains(expected);
@@ -177,7 +177,7 @@ public static void assertContains(Iterable<?> actual, Object expected) {
     }
   }
 
-  public static void assertContainsAllOf(Iterable<?> actual, Object... expected) {
+  public static void assertContainsAllOf(Iterable<?> actual, @Nullable Object... expected) {
     List<Object> expectedList = new ArrayList<>(asList(expected));
 
     for (Object o : actual) {
diff --git a/android/guava-testlib/src/com/google/common/escape/testing/EscaperAsserts.java b/android/guava-testlib/src/com/google/common/escape/testing/EscaperAsserts.java
index 31ac2015dd04..8f9ba92bc3f7 100644
--- a/android/guava-testlib/src/com/google/common/escape/testing/EscaperAsserts.java
+++ b/android/guava-testlib/src/com/google/common/escape/testing/EscaperAsserts.java
@@ -17,6 +17,7 @@
 package com.google.common.escape.testing;
 
 import static com.google.common.escape.Escapers.computeReplacement;
+import static org.junit.Assert.assertThrows;
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.escape.CharEscaper;
@@ -40,16 +41,12 @@ private EscaperAsserts() {}
    *
    * @param escaper the non-null escaper to test
    */
+  @SuppressWarnings("NullArgumentForNonNullParameter") // test of a bogus call
   public static void assertBasic(Escaper escaper) throws IOException {
     // Escapers operate on characters: no characters, no escaping.
     Assert.assertEquals("", escaper.escape(""));
     // Assert that escapers throw null pointer exceptions.
-    try {
-      escaper.escape((String) null);
-      Assert.fail("exception not thrown when escaping a null string");
-    } catch (NullPointerException e) {
-      // pass
-    }
+    assertThrows(NullPointerException.class, () -> escaper.escape(null));
   }
 
   /**
@@ -60,7 +57,6 @@ public static void assertBasic(Escaper escaper) throws IOException {
    * @param c the character to escape
    */
   public static void assertEscaping(CharEscaper escaper, String expected, char c) {
-
     String escaped = computeReplacement(escaper, c);
     Assert.assertNotNull(escaped);
     Assert.assertEquals(expected, escaped);
@@ -74,7 +70,6 @@ public static void assertEscaping(CharEscaper escaper, String expected, char c)
    * @param cp the Unicode code point to escape
    */
   public static void assertEscaping(UnicodeEscaper escaper, String expected, int cp) {
-
     String escaped = computeReplacement(escaper, cp);
     Assert.assertNotNull(escaped);
     Assert.assertEquals(expected, escaped);
@@ -110,7 +105,6 @@ public static void assertUnescaped(UnicodeEscaper escaper, int cp) {
    */
   public static void assertUnicodeEscaping(
       UnicodeEscaper escaper, String expected, char hi, char lo) {
-
     int cp = Character.toCodePoint(hi, lo);
     String escaped = computeReplacement(escaper, cp);
     Assert.assertNotNull(escaped);
diff --git a/guava-testlib/src/com/google/common/collect/testing/Helpers.java b/guava-testlib/src/com/google/common/collect/testing/Helpers.java
index 24cb640427af..bfc1ae1eccac 100644
--- a/guava-testlib/src/com/google/common/collect/testing/Helpers.java
+++ b/guava-testlib/src/com/google/common/collect/testing/Helpers.java
@@ -127,7 +127,7 @@ public static void assertEqualInOrder(Iterable<?> expected, Iterable<?> actual)
     }
   }
 
-  public static void assertContentsInOrder(Iterable<?> actual, Object... expected) {
+  public static void assertContentsInOrder(Iterable<?> actual, @Nullable Object... expected) {
     assertEqualInOrder(asList(expected), actual);
   }
 
@@ -155,11 +155,11 @@ public static void assertEqualIgnoringOrder(Iterable<?> expected, Iterable<?> ac
     assertTrue("unexpected elements: " + act, act.isEmpty());
   }
 
-  public static void assertContentsAnyOrder(Iterable<?> actual, Object... expected) {
+  public static void assertContentsAnyOrder(Iterable<?> actual, @Nullable Object... expected) {
     assertEqualIgnoringOrder(asList(expected), actual);
   }
 
-  public static void assertContains(Iterable<?> actual, Object expected) {
+  public static void assertContains(Iterable<?> actual, @Nullable Object expected) {
     boolean contained = false;
     if (actual instanceof Collection) {
       contained = ((Collection<?>) actual).contains(expected);
@@ -177,7 +177,7 @@ public static void assertContains(Iterable<?> actual, Object expected) {
     }
   }
 
-  public static void assertContainsAllOf(Iterable<?> actual, Object... expected) {
+  public static void assertContainsAllOf(Iterable<?> actual, @Nullable Object... expected) {
     List<Object> expectedList = new ArrayList<>(asList(expected));
 
     for (Object o : actual) {
diff --git a/guava-testlib/src/com/google/common/escape/testing/EscaperAsserts.java b/guava-testlib/src/com/google/common/escape/testing/EscaperAsserts.java
index 31ac2015dd04..8f9ba92bc3f7 100644
--- a/guava-testlib/src/com/google/common/escape/testing/EscaperAsserts.java
+++ b/guava-testlib/src/com/google/common/escape/testing/EscaperAsserts.java
@@ -17,6 +17,7 @@
 package com.google.common.escape.testing;
 
 import static com.google.common.escape.Escapers.computeReplacement;
+import static org.junit.Assert.assertThrows;
 
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.escape.CharEscaper;
@@ -40,16 +41,12 @@ private EscaperAsserts() {}
    *
    * @param escaper the non-null escaper to test
    */
+  @SuppressWarnings("NullArgumentForNonNullParameter") // test of a bogus call
   public static void assertBasic(Escaper escaper) throws IOException {
     // Escapers operate on characters: no characters, no escaping.
     Assert.assertEquals("", escaper.escape(""));
     // Assert that escapers throw null pointer exceptions.
-    try {
-      escaper.escape((String) null);
-      Assert.fail("exception not thrown when escaping a null string");
-    } catch (NullPointerException e) {
-      // pass
-    }
+    assertThrows(NullPointerException.class, () -> escaper.escape(null));
   }
 
   /**
@@ -60,7 +57,6 @@ public static void assertBasic(Escaper escaper) throws IOException {
    * @param c the character to escape
    */
   public static void assertEscaping(CharEscaper escaper, String expected, char c) {
-
     String escaped = computeReplacement(escaper, c);
     Assert.assertNotNull(escaped);
     Assert.assertEquals(expected, escaped);
@@ -74,7 +70,6 @@ public static void assertEscaping(CharEscaper escaper, String expected, char c)
    * @param cp the Unicode code point to escape
    */
   public static void assertEscaping(UnicodeEscaper escaper, String expected, int cp) {
-
     String escaped = computeReplacement(escaper, cp);
     Assert.assertNotNull(escaped);
     Assert.assertEquals(expected, escaped);
@@ -110,7 +105,6 @@ public static void assertUnescaped(UnicodeEscaper escaper, int cp) {
    */
   public static void assertUnicodeEscaping(
       UnicodeEscaper escaper, String expected, char hi, char lo) {
-
     int cp = Character.toCodePoint(hi, lo);
     String escaped = computeReplacement(escaper, cp);
     Assert.assertNotNull(escaped);