update docs

Author: dlarocque

google-cloud-firestore/src/main/java/com/google/cloud/firestore/pipeline/expressions/Expression.java

@@ -2050,6 +2050,9 @@ public static Expression mapSet(
 
   /**
    * Creates an expression that returns the keys of a map.
+   * 
+   * <p>While the backend generally preserves insertion order, relying on the order of the output
+   * array is not guaranteed and should be avoided.
    *
    * @param mapExpr The expression representing the map to get the keys of.
    * @return A new {@link Expression} representing the keys of the map.
@@ -2061,6 +2064,9 @@ public static Expression mapKeys(Expression mapExpr) {
 
   /**
    * Creates an expression that returns the keys of a map.
+   * 
+   * <p>While the backend generally preserves insertion order, relying on the order of the output
+   * array is not guaranteed and should be avoided.
    *
    * @param mapField The map field to get the keys of.
    * @return A new {@link Expression} representing the keys of the map.
@@ -2086,6 +2092,9 @@ public static Expression mapValues(Expression mapExpr) {
 
   /**
    * Creates an expression that returns the values of a map.
+   * 
+   * <p>While the backend generally preserves insertion order, relying on the order of the output
+   * array is not guaranteed and should be avoided.
    *
    * @param mapField The map field to get the values of.
    * @return A new {@link Expression} representing the values of the map.
@@ -2112,6 +2121,9 @@ public static Expression mapEntries(Expression mapExpr) {
 
   /**
    * Creates an expression that returns the entries of a map as an array of maps.
+   * 
+   * <p>While the backend generally preserves insertion order, relying on the order of the output
+   * array is not guaranteed and should be avoided.
    *
    * @param mapField The map field to get the entries of.
    * @return A new {@link Expression} representing the entries of the map.