Update Javadoc to match implementation details.

src/main/java/org/apache/commons/lang3/tuple/ImmutablePair.java

@@ -115,15 +115,15 @@ public final class ImmutablePair<L, R> extends Pair<L, R> {
     }
 
     /**
-     * <p>Creates an immutable pair from an existing pair.</p>
+     * <p>Creates an immutable pair from a map entry.</p>
      *
      * <p>This factory allows the pair to be created using inference to
      * obtain the generic types.</p>
      *
      * @param <L> the left element type
      * @param <R> the right element type
-     * @param pair the existing pair.
+     * @param pair the existing map entry.
-     * @return a pair formed from the two parameters, not null
+     * @return a pair formed from the map entry
      * @since 3.10
      */
     public static <L, R> ImmutablePair<L, R> of(final Map.Entry<L, R> pair) {

src/main/java/org/apache/commons/lang3/tuple/MutablePair.java

@@ -75,15 +75,15 @@ public class MutablePair<L, R> extends Pair<L, R> {
     }
 
     /**
-     * <p>Creates a mutable pair from an existing pair.</p>
+     * <p>Creates a mutable pair from a map entry.</p>
      *
      * <p>This factory allows the pair to be created using inference to
      * obtain the generic types.</p>
      *
      * @param <L> the left element type
      * @param <R> the right element type
-     * @param pair the existing pair.
+     * @param pair the existing map entry.
-     * @return a pair formed from the two parameters, not null
+     * @return a pair formed from the map entry
      */
     public static <L, R> MutablePair<L, R> of(final Map.Entry<L, R> pair) {
         final L left;

src/main/java/org/apache/commons/lang3/tuple/Pair.java

@@ -105,15 +105,15 @@ public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L,
     }
 
     /**
-     * <p>Creates an immutable pair from an existing pair.</p>
+     * <p>Creates an immutable pair from a map entry.</p>
      *
      * <p>This factory allows the pair to be created using inference to
      * obtain the generic types.</p>
      *
      * @param <L> the left element type
      * @param <R> the right element type
-     * @param pair the existing pair.
+     * @param pair the map entry.
-     * @return a pair formed from the two parameters, not null
+     * @return a pair formed from the map entry
      * @since 3.10
      */
     public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {