[FIX] Regression in map implementation. Closes #2615

Author: ChristianGruen

basex-core/src/main/java/org/basex/query/value/map/TrieBranch.java

@@ -70,6 +70,9 @@ TrieNode remove(final int hs, final int lv, final TrieUpdate update) throws Quer
     } else {
       nu = used;
     }
+    // single leaf remains
+    if(size == 2) return nsub;
+    // create new array, replace child
     final TrieNode[] ks = kids.clone();
     ks[k] = nsub;
     return new TrieBranch(ks, nu, size - 1);

basex-core/src/test/java/org/basex/query/func/MapModuleTest.java

@@ -515,6 +515,10 @@ record = "declare record local:x(x as xs:integer);";
     // GH-2438
     query("let $f := fn($map) { fold-left(map:keys($map), $map, map:remove#2) } " +
         "return $f({ 'a': () })", "{}");
+    // GH-2615
+    query("{ 'aa': 1, 'bb': 2, 'cc': 3 } => map:remove('aa') => map:remove('bb')", "{\"cc\":3}");
+    query("{ 'aa': 1, 'bb': 2, 'cc': 3 } => map:remove('aa') => map:remove('cc')", "{\"bb\":2}");
+    query("{ 'aa': 1, 'bb': 2, 'cc': 3 } => map:remove('bb') => map:remove('cc')", "{\"aa\":1}");
   }
 
   /** Test method. */