Use isEmpty().

src/main/java/org/apache/commons/lang3/StringUtils.java

@@ -6707,7 +6707,7 @@ public class StringUtils {
             final Set<String> searchSet = new HashSet<>(Arrays.asList(searchList));
             final Set<String> replacementSet = new HashSet<>(Arrays.asList(replacementList));
             searchSet.retainAll(replacementSet);
-            if (searchSet.size() > 0) {
+            if (!searchSet.isEmpty()) {
                 throw new IllegalStateException("Aborting to protect against StackOverflowError - " +
                         "output of one loop is the input of another");
             }

src/main/java/org/apache/commons/lang3/text/StrBuilder.java

@@ -282,6 +282,19 @@ public class StrBuilder implements CharSequence, Appendable, Serializable, Build
         return size == 0;
     }
 
+    /**
+     * Checks is the string builder is not empty (convenience Collections API style method).
+     * <p>
+     * This method is the same as checking {@link #length()} and is provided to match the
+     * API of Collections.
+     *
+     * @return {@code true} if the size is greater than {@code 0}.
+     * @since 3.12
+     */
+    public boolean isNotEmpty() {
+        return size > 0;
+    }
+
     /**
      * Clears the string builder (convenience Collections API style method).
      * <p>
@@ -1390,7 +1403,7 @@ public class StrBuilder implements CharSequence, Appendable, Serializable, Build
      * @since 2.3
      */
     public StrBuilder appendSeparator(final char separator) {
-        if (size() > 0) {
+        if (isNotEmpty()) {
             append(separator);
         }
         return this;
@@ -1408,7 +1421,7 @@ public class StrBuilder implements CharSequence, Appendable, Serializable, Build
      * @since 2.5
      */
     public StrBuilder appendSeparator(final char standard, final char defaultIfEmpty) {
-        if (size() > 0) {
+        if (isNotEmpty()) {
             append(standard);
         } else {
             append(defaultIfEmpty);

src/test/java/org/apache/commons/lang3/ThreadUtilsTest.java

@@ -127,12 +127,12 @@ public class ThreadUtilsTest {
 
     @Test
     public void testAtLeastOneThreadExists() {
-        assertTrue(ThreadUtils.getAllThreads().size() > 0);
+        assertFalse(ThreadUtils.getAllThreads().isEmpty());
     }
 
     @Test
     public void testAtLeastOneThreadGroupsExists() {
-        assertTrue(ThreadUtils.getAllThreadGroups().size() > 0);
+        assertFalse(ThreadUtils.getAllThreadGroups().isEmpty());
     }
 
     @Test