diff --git a/.idea/codeStyles/codeStyleConfig.xml b/.idea/codeStyles/codeStyleConfig.xml
deleted file mode 100644
index a55e7a179b..0000000000
--- a/.idea/codeStyles/codeStyleConfig.xml
+++ /dev/null
@@ -1,5 +0,0 @@
-<component name="ProjectCodeStyleConfiguration">
-  <state>
-    <option name="PREFERRED_PROJECT_CODE_STYLE" value="Default" />
-  </state>
-</component>
\ No newline at end of file
diff --git a/user/super/com/google/gwt/emul/java/lang/Character.java b/user/super/com/google/gwt/emul/java/lang/Character.java
index 4b01e4d43d..d675b1719e 100644
--- a/user/super/com/google/gwt/emul/java/lang/Character.java
+++ b/user/super/com/google/gwt/emul/java/lang/Character.java
@@ -322,7 +322,7 @@ private static boolean isWhitespace(String ch) {
       // the Java definition includes separators.
       whitespaceRegex =
           new NativeRegExp(
-              "[\\u1680\\u180E\\u2000-\\u2006\\u2008-\\u200A\\u2028\\u2029\\u205F\\u3000\\uFEFF]"
+              "[\\u1680\\u2000-\\u2006\\u2008-\\u200A\\u2028\\u2029\\u205F\\u3000]"
                   + "|[\\t-\\r ]"
                   + "|[\\x1C-\\x1F]");
     }
diff --git a/user/super/com/google/gwt/emul/java/lang/String.java b/user/super/com/google/gwt/emul/java/lang/String.java
index ff166b3a32..e0d6ffda72 100644
--- a/user/super/com/google/gwt/emul/java/lang/String.java
+++ b/user/super/com/google/gwt/emul/java/lang/String.java
@@ -16,6 +16,7 @@
 
 package java.lang;
 
+import static javaemul.internal.InternalPreconditions.checkArgument;
 import static javaemul.internal.InternalPreconditions.checkCriticalStringBounds;
 import static javaemul.internal.InternalPreconditions.checkNotNull;
 import static javaemul.internal.InternalPreconditions.checkStringBounds;
@@ -782,13 +783,11 @@ public boolean isBlank() {
   }
 
   public Stream<String> lines() {
-    return StreamSupport.stream(new LinesSpliterator(this), false);
+    return StreamSupport.stream(new LinesSpliterator(), false);
   }
 
   public String repeat(int count) {
-    if (count < 0) {
-      throw new IllegalArgumentException("count is negative: " + count);
-    }
+    checkArgument(count >= 0, "count is negative: " + count);
     return asNativeString().repeat(count);
   }
 
@@ -812,15 +811,13 @@ private int getTrailingWhitespaceLength() {
     return length;
   }
 
-  private static class LinesSpliterator extends Spliterators.AbstractSpliterator<String> {
+  private class LinesSpliterator extends Spliterators.AbstractSpliterator<String> {
     private int nextIndex = 0;
-    private String content;
-    int rPosition = -2;
-    int nPosition = -2;
+    private int rPosition = -1;
+    private int nPosition = -1;
 
-    private LinesSpliterator(String content) {
+    private LinesSpliterator() {
       super(Long.MAX_VALUE, Spliterator.IMMUTABLE | Spliterator.ORDERED);
-      this.content = content;
     }
 
     @Override
@@ -832,17 +829,17 @@ public boolean tryAdvance(Consumer<? super String> action) {
         nPosition = cappedIndexOf('\n');
       }
       int lineEnd = Math.min(nPosition, rPosition);
-      action.accept(content.substring(nextIndex, lineEnd));
+      action.accept(substring(nextIndex, lineEnd));
       nextIndex = lineEnd + 1;
       if (nPosition == rPosition + 1) {
         nextIndex++;
       }
-      return nextIndex < content.length();
+      return nextIndex < length();
     }
 
     private int cappedIndexOf(char c) {
-      int index = content.indexOf(c);
-      return index == -1 ? content.length() : index;
+      int index = indexOf(c);
+      return index == -1 ? length() : index;
     }
   }
 
diff --git a/user/test/com/google/gwt/emultest/java/lang/CharacterTest.java b/user/test/com/google/gwt/emultest/java/lang/CharacterTest.java
index 41c6f247ec..a2ccc9e6ad 100644
--- a/user/test/com/google/gwt/emultest/java/lang/CharacterTest.java
+++ b/user/test/com/google/gwt/emultest/java/lang/CharacterTest.java
@@ -360,7 +360,8 @@ public void testIsWhitepace() {
     char[] nonBreakingSpaceSeparators = {
         '\u00A0', // NO-BREAK SPACE.
         '\u2007', // FIGURE SPACE.
-        '\u202F' // NARROW NO-BREAK SPACE.
+        '\u202F', // NARROW NO-BREAK SPACE.
+        '\uFFEF'  // ZERO WIDTH NO-BREAK SPACE.
     };
 
     char[] specialCases = {
@@ -379,7 +380,8 @@ public void testIsWhitepace() {
         'a', // LATIN SMALL LETTER A.
         'B', // LATIN CAPITAL LETTER B.
         '_', // LOW LINE.
-        '\u2500' // BOX DRAWINGS LIGHT HORIZONTAL.
+        '\u2500', // BOX DRAWINGS LIGHT HORIZONTAL.
+        '\u180E', // MONGOLIAN VOWEL SEPARATOR, was considered whitespace in Java 8.
     };
 
     int[] supplementaryCounterExamples = {
diff --git a/user/test/com/google/gwt/emultest/java/lang/StringTest.java b/user/test/com/google/gwt/emultest/java/lang/StringTest.java
index 4b08a45eee..1600f8568a 100644
--- a/user/test/com/google/gwt/emultest/java/lang/StringTest.java
+++ b/user/test/com/google/gwt/emultest/java/lang/StringTest.java
@@ -895,6 +895,7 @@ public void testTrim() {
 
     // JavaScript would trim \u2029 and other unicode whitespace type characters; but Java wont
     trimRightAssertEquals("\u2029abc\u00a0","\u2029abc\u00a0");
+    trimRightAssertEquals("\uffefx\u180e", "\uffefx\u180e ");
   }
 
   public void testUpperCase() {
diff --git a/user/test/com/google/gwt/emultest/java11/lang/StringTest.java b/user/test/com/google/gwt/emultest/java11/lang/StringTest.java
index 34544e402a..af2e44abdc 100644
--- a/user/test/com/google/gwt/emultest/java11/lang/StringTest.java
+++ b/user/test/com/google/gwt/emultest/java11/lang/StringTest.java
@@ -33,27 +33,40 @@ public void testIsBlank() {
   }
 
   public void testStrip() {
-    assertEquals("", "".strip());
-    assertEquals("", "  ".strip());
-    assertEquals("x", " x ".strip());
-    assertEquals("x", "\u001cx\u001c".strip());
-    assertEquals("\u00a0x\u00a0", "\u00a0x\u00a0 ".strip());
+    stripRightAsssertEquals("", "");
+    stripRightAsssertEquals("", "  ");
+    stripRightAsssertEquals("x", " x ");
+    stripRightAsssertEquals("x", "\u001cx\u001c");
+    stripRightAsssertEquals("\u00a0x\u00a0", "\u00a0x\u00a0 ");
+    stripRightAsssertEquals("\uffefx\u180e", "\uffefx\u180e ");
   }
 
   public void testStripLeading() {
-    assertEquals("", "".stripLeading());
-    assertEquals("", "  ".stripLeading());
-    assertEquals("x ", " x ".stripLeading());
-    assertEquals("x\u001c", "\u001cx\u001c".stripLeading());
-    assertEquals("\u00a0x\u00a0", "\u00a0x\u00a0".stripLeading());
+    stripRightLeadingAsssertEquals("", "");
+    stripRightLeadingAsssertEquals("", "  ");
+    stripRightLeadingAsssertEquals("x ", " x ");
+    stripRightLeadingAsssertEquals("x\u001c", "\u001cx\u001c");
+    stripRightLeadingAsssertEquals("\u00a0x\u00a0", "\u00a0x\u00a0");
   }
 
   public void testStripTrailing() {
-    assertEquals("", "".stripTrailing());
-    assertEquals("", "  ".stripTrailing());
-    assertEquals(" x", " x ".stripTrailing());
-    assertEquals("\u001cx", "\u001cx\u001c".stripTrailing());
-    assertEquals("\u00a0x\u00a0", "\u00a0x\u00a0 ".stripTrailing());
+    stripRightTrailingAsssertEquals("", "");
+    stripRightTrailingAsssertEquals("", "  ");
+    stripRightTrailingAsssertEquals(" x", " x ");
+    stripRightTrailingAsssertEquals("\u001cx", "\u001cx\u001c");
+    stripRightTrailingAsssertEquals("\u00a0x\u00a0", "\u00a0x\u00a0 ");
+  }
+
+  private void stripRightAsssertEquals(String expected, String arg) {
+    assertEquals(expected, arg.strip())
+  }
+
+  private void stripRightLeadingAsssertEquals(String expected, String arg) {
+    assertEquals(expected, arg.stripLeading())
+  }
+
+  private void stripRightTrailingAsssertEquals(String expected, String arg) {
+    assertEquals(expected, arg.stripTrailing())
   }
 
   public void testRepeat() {