Added empty string example for isMixedCase method.
diff --git a/src/main/java/org/apache/commons/lang3/StringUtils.java b/src/main/java/org/apache/commons/lang3/StringUtils.java
index 0b6fed6..0f58951 100644
--- a/src/main/java/org/apache/commons/lang3/StringUtils.java
+++ b/src/main/java/org/apache/commons/lang3/StringUtils.java
@@ -3605,6 +3605,7 @@
      * <pre>
      * StringUtils.isMixedCase(null)    = false
      * StringUtils.isMixedCase("")      = false
+     * StringUtils.isMixedCase(" ")     = false
      * StringUtils.isMixedCase("ABC")   = false
      * StringUtils.isMixedCase("abc")   = false
      * StringUtils.isMixedCase("aBc")   = true