diff --git a/metatype/src/main/java/org/apache/felix/metatype/AD.java b/metatype/src/main/java/org/apache/felix/metatype/AD.java
index 1a2ff9a..a726a20 100644
--- a/metatype/src/main/java/org/apache/felix/metatype/AD.java
+++ b/metatype/src/main/java/org/apache/felix/metatype/AD.java
@@ -224,7 +224,7 @@
      * NOTE: this method is depending on the value of {@link #getCardinality()}! Make sure that the
      * cardinality is properly set <b>before</b> calling this method.
      * </p>
-     * 
+     *
      * @param defaultValue the default value to set, as encoded string-value (using comma's as separator), can be <code>null</code>.
      */
     public void setDefaultValue(String defaultValue)
@@ -314,8 +314,8 @@
             return new String[] { "" };
         }
 
-        List strings = new ArrayList();
-        StringBuffer sb = new StringBuffer();
+        List<String> strings = new ArrayList<>();
+        StringBuilder sb = new StringBuilder();
 
         int length = listString.length();
         boolean escaped = false;
@@ -383,7 +383,7 @@
         // Always add the last string, as it contains everything after the last comma...
         strings.add(sb.toString());
 
-        return (String[]) strings.toArray(new String[strings.size()]);
+        return strings.toArray(new String[strings.size()]);
     }
 
     protected Comparable convertToType(final String value)
@@ -477,6 +477,7 @@
             value = Boolean.valueOf(boolValue).booleanValue();
         }
 
+        @Override
         public int compareTo(Object obj)
         {
             ComparableBoolean cb = (ComparableBoolean) obj;
diff --git a/metatype/src/main/java/org/apache/felix/metatype/ADValidator.java b/metatype/src/main/java/org/apache/felix/metatype/ADValidator.java
index 60b35a0..a6224af 100644
--- a/metatype/src/main/java/org/apache/felix/metatype/ADValidator.java
+++ b/metatype/src/main/java/org/apache/felix/metatype/ADValidator.java
@@ -27,29 +27,29 @@
 /**
  * Provides various validation routines used by the {@link AD#validate(String)}
  * method.
- * 
+ *
  * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a>
  */
 final class ADValidator
 {
     /**
-     * Validates a given input string according to the type specified by the given attribute 
+     * Validates a given input string according to the type specified by the given attribute
      * definition.
      * <p>
      * The validation is done in the following way:
      * </p>
      * <ul>
-     * <li>If the input is undefined (ie. <code>null</code>), and the attribute is mandatory, the 
-     * validation fails due to a missing value. If the attribute is optional, the input is 
+     * <li>If the input is undefined (ie. <code>null</code>), and the attribute is mandatory, the
+     * validation fails due to a missing value. If the attribute is optional, the input is
      * accepted;</li>
      * <li>If the input represents a <em>boolean</em> value, it is tested whether it is defined (in
      * case of non-zero cardinality) and represents either <tt>"true"</tt> or <tt>"false"</tt>. The
      * minimum and maximum parameters are <b>not</b> used in this validation;</li>
-     * <li>If the input represents a <em>character</em> value, it is tested whether it is defined 
-     * (in case of non-zero cardinality). The character value must be defined within the character 
+     * <li>If the input represents a <em>character</em> value, it is tested whether it is defined
+     * (in case of non-zero cardinality). The character value must be defined within the character
      * range specified by the minimum and maximum parameters (if defined);</li>
      * <li>If the input represents a <em>numeric</em> value, it is tested whether it is defined (in
-     * case of non-zero cardinality). The numeric value must be defined within the numeric range 
+     * case of non-zero cardinality). The numeric value must be defined within the numeric range
      * specified by the minimum and maximum parameters (if defined);</li>
      * <li>If the input represents a <em>string</em> or <em>password</em>, it is tested whether it
      * is defined (in case of non-zero cardinality). The length of the string value must be in the
@@ -57,9 +57,9 @@
      * </ul>
      * <p>
      * For all types of attributes, if it defines option values, the input should be present as one
-     * of the defined option values. 
+     * of the defined option values.
      * </p>
-     * 
+     *
      * @param ad
      *            the attribute definition to use in the validation;
      * @param rawInput
@@ -122,7 +122,7 @@
 
     /**
      * Searches for a given search value in a given array of options.
-     * 
+     *
      * @param searchValue
      *            the value to search for;
      * @param optionValues
@@ -152,7 +152,7 @@
 
     /**
      * Parses a given string value into a numeric type.
-     * 
+     *
      * @param type
      *            the type to parse;
      * @param value
@@ -195,7 +195,7 @@
     /**
      * Parses a given string value as character, allowing <code>null</code>
      * -values and empty values to be given as input.
-     * 
+     *
      * @param value
      *            the value to parse as character, can be <code>null</code> or
      *            an empty value.
@@ -212,10 +212,10 @@
     }
 
     /**
-     * Parses a given string value as numeric value, allowing 
-     * <code>null</code>-values and invalid numeric values to be given as 
+     * Parses a given string value as numeric value, allowing
+     * <code>null</code>-values and invalid numeric values to be given as
      * input.
-     * 
+     *
      * @param type the type of number, should only be a numeric type;
      * @param value
      *            the value to parse as integer, can be <code>null</code> or a
@@ -241,7 +241,7 @@
 
     /**
      * Validates a given input string as boolean value.
-     * 
+     *
      * @param ad
      *            the attribute definition to use in the validation;
      * @param input
@@ -278,7 +278,7 @@
 
     /**
      * Validates a given input string as character value.
-     * 
+     *
      * @param ad
      *            the attribute definition to use in the validation;
      * @param input
@@ -332,7 +332,7 @@
 
     /**
      * Validates a given input string as numeric value.
-     * 
+     *
      * @param ad
      *            the attribute definition to use in the validation;
      * @param input
@@ -387,7 +387,7 @@
 
     /**
      * Validates a given input string as string (or password).
-     * 
+     *
      * @param ad
      *            the attribute definition to use in the validation;
      * @param input
@@ -406,12 +406,9 @@
         for (int i = 0; i < input.length; i++)
         {
             String value = input[i];
-            int length = (value == null) ? 0 : value.length();
-
-            if (ad.isRequired() && ((value == null) || (length == 0)))
+            final int length = value == null ? 0 : value.length();
+            if (ad.isRequired() && value == null)
             {
-                // Possible if the cardinality != 0 and input was something like
-                // "0,,1"...
                 return AD.VALIDATE_MISSING;
             }
             // Check whether the minimum length is adhered for all values...
diff --git a/metatype/src/test/java/org/apache/felix/metatype/ADTest.java b/metatype/src/test/java/org/apache/felix/metatype/ADTest.java
index c830cfe..aa82648 100644
--- a/metatype/src/test/java/org/apache/felix/metatype/ADTest.java
+++ b/metatype/src/test/java/org/apache/felix/metatype/ADTest.java
@@ -21,10 +21,10 @@
 import java.util.HashMap;
 import java.util.Map;
 
-import junit.framework.TestCase;
-
 import org.osgi.service.metatype.AttributeDefinition;
 
+import junit.framework.TestCase;
+
 /**
  * The <code>ADTest</code> class tests the static helper methods of the
  * {@link AD} class.
@@ -255,11 +255,9 @@
         ad.setDefaultValue("");
         assertArrayEquals(new String[] { "" }, ad.getDefaultValue());
 
-        // corner case: in case of required values, an empty default makes no sense
-        // for single values, hence that the empty default is coerced into null...
         ad.setRequired(true);
         ad.setDefaultValue("");
-        assertNull(ad.getDefaultValue());
+        assertArrayEquals(new String[] { "" }, ad.getDefaultValue());
     }
 
     /**
@@ -284,11 +282,9 @@
         ad.setDefaultValue("");
         assertArrayEquals(new String[] { "" }, ad.getDefaultValue());
 
-        // corner case: in case of required values, an empty default is coerced
-        // into a empty array...
         ad.setRequired(true);
         ad.setDefaultValue("");
-        assertArrayEquals(new String[0], ad.getDefaultValue());
+        assertArrayEquals(new String[] {""}, ad.getDefaultValue());
     }
 
     private static void assertArrayEquals(String[] a, String[] b)
@@ -299,4 +295,12 @@
             assertEquals(a[i], b[i]);
         }
     }
+
+    public void testSplitList() {
+        final String[] array = AD.splitList("321, , 123");
+        assertEquals(3, array.length);
+        assertEquals("321", array[0]);
+        assertEquals("", array[1]);
+        assertEquals("123", array[2]);
+    }
 }
diff --git a/metatype/src/test/java/org/apache/felix/metatype/ADValidatorTest.java b/metatype/src/test/java/org/apache/felix/metatype/ADValidatorTest.java
index 33c02c3..5b7c11d 100644
--- a/metatype/src/test/java/org/apache/felix/metatype/ADValidatorTest.java
+++ b/metatype/src/test/java/org/apache/felix/metatype/ADValidatorTest.java
@@ -27,7 +27,7 @@
 
 /**
  * Test cases for {@link ADValidator}.
- * 
+ *
  * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a>
  */
 public class ADValidatorTest extends TestCase
@@ -150,7 +150,7 @@
         // adhere maximal values
         assertEquals("", ADValidator.validate(ad, "c, d, e"));
 
-        Map options = new HashMap();
+        Map<String, String> options = new HashMap<>();
         options.put("b", "B");
         options.put("c", "C");
         options.put("d", "D");
@@ -349,18 +349,19 @@
 
         // optional value
         assertEquals("", ADValidator.validate(ad, null));
-        // 2nd value is missing; but that's ok
+        // 2nd value is empty; but that's ok
         assertEquals("", ADValidator.validate(ad, "321, , 123"));
 
         ad.setRequired(true);
         ad.setMin("3");
 
+
         // mandatory value
         assertEquals(AD.VALIDATE_MISSING, ADValidator.validate(ad, null));
-        // 2nd value is missing
-        assertEquals(AD.VALIDATE_MISSING, ADValidator.validate(ad, "321, , 123"));
         // 2nd value is too short
         assertEquals(AD.VALIDATE_LESS_THAN_MINIMUM, ADValidator.validate(ad, "321,12,123"));
+        // 2nd value is empty and therefore too short
+        assertEquals(AD.VALIDATE_LESS_THAN_MINIMUM, ADValidator.validate(ad, "321, , 123"));
         // adhere minimum lengths
         assertEquals("", ADValidator.validate(ad, "123, 123, 123"));
         // adhere maximum lengths