Make Java 11 Javadoc happy by replacing <tt> tags with standard Javadoc

<code> tags.

src/main/java/org/apache/commons/collections4/CollectionUtils.java

@@ -264,8 +264,8 @@ public class CollectionUtils {
      * <p>
      * The cardinality of each element <i>e</i> in the returned
      * {@link Collection} will be equal to
-     * <tt>max(cardinality(<i>e</i>,<i>a</i>),cardinality(<i>e</i>,<i>b</i>)) - min(cardinality(<i>e</i>,<i>a</i>),
-     * cardinality(<i>e</i>,<i>b</i>))</tt>.
+     * <code>max(cardinality(<i>e</i>,<i>a</i>),cardinality(<i>e</i>,<i>b</i>)) - min(cardinality(<i>e</i>,<i>a</i>),
+     * cardinality(<i>e</i>,<i>b</i>))</code>.
      * <p>
      * This is equivalent to
      * {@code {@link #subtract subtract}({@link #union union(a,b)},{@link #intersection intersection(a,b)})}

src/main/java/org/apache/commons/collections4/Get.java

@@ -63,7 +63,7 @@ public interface Get<K, V> {
     /**
      * @param key key whose mapping is to be removed from the map
      * @return the previous value associated with <code>key</code>, or
-     *         <code>null</tt> if there was no mapping for <tt>key</code>.
+     *         <code>null</code> if there was no mapping for <code>key</code>.
      * @see java.util.Map#remove(Object)
      */
     V remove(Object key);

src/main/java/org/apache/commons/collections4/ListUtils.java

@@ -219,8 +219,8 @@ public class ListUtils {
      * {@code true} if and only if both
      * lists have the same size, and all corresponding pairs of elements in
      * the two lists are <i>equal</i>.  (Two elements {@code e1} and
-     * {@code e2} are <i>equal</i> if <tt>(e1==null ? e2==null :
-     * e1.equals(e2))</tt>.)  In other words, two lists are defined to be
+     * {@code e2} are <i>equal</i> if <code>(e1==null ? e2==null :
+     * e1.equals(e2))</code>.)  In other words, two lists are defined to be
      * equal if they contain the same elements in the same order.  This
      * definition ensures that the equals method works properly across
      * different implementations of the {@code List} interface.

src/main/java/org/apache/commons/collections4/MultiSet.java

@@ -240,7 +240,7 @@ public interface MultiSet<E> extends Collection<E> {
          * and the two entries represent the same element with the same
          * number of occurrences.
          * <p>
-         * More formally, two entries <code>e1</tt> and <tt>e2</code> represent
+         * More formally, two entries <code>e1</code> and <code>e2</code> represent
          * the same mapping if
          * <pre>
          *     (e1.getElement()==null ? e2.getElement()==null

src/main/java/org/apache/commons/collections4/Put.java

@@ -47,9 +47,9 @@ public interface Put<K, V> {
      * @param key key with which the specified value is to be associated
      * @param value value to be associated with the specified key
      * @return the previous value associated with <code>key</code>, or
-     *         <code>null</tt> if there was no mapping for <tt>key</code>.
+     *         <code>null</code> if there was no mapping for <code>key</code>.
      *         (A <code>null</code> return can also indicate that the map
-     *         previously associated <code>null</tt> with <tt>key</code>,
+     *         previously associated <code>null</code> with <code>key</code>,
      *         if the implementation supports <code>null</code> values.)
      * @see Map#put(Object, Object)
      */

src/main/java/org/apache/commons/collections4/map/CompositeMap.java

@@ -268,8 +268,8 @@ public class CompositeMap<K, V> extends AbstractIterableMap<K, V> implements Ser
      * operation may be used to distinguish these two cases.
      *
      * <p>More formally, if this map contains a mapping from a key
-     * {@code k} to a value {@code v} such that <tt>(key==null ? k==null :
-     * key.equals(k))</tt>, then this method returns {@code v}; otherwise
+     * {@code k} to a value {@code v} such that <code>(key==null ? k==null :
+     * key.equals(k))</code>, then this method returns {@code v}; otherwise
      * it returns {@code null}.  (There can be at most one such mapping.)
      *
      * @param key key whose associated value is to be returned.