Fix requested from review.

Author: leerho

src/test/java/org/apache/datasketches/memory/internal/AllocateDirectMapMemoryTest.java

@@ -49,7 +49,7 @@ public void simpleMap() throws IOException {
       arena.close();
     } //The Try-With-Resources will throw since it is already closed
     catch (IllegalStateException e) { /* OK */ }
-    assertFalse(mem.isAlive());
+    if (mem != null) { assertFalse(mem.isAlive()); }
   }
 
   @Test
@@ -87,7 +87,7 @@ public void testMapAndMultipleClose() throws IOException {
       } //a close inside the TWR block will throw here
     }
     catch (IllegalStateException e) { /* expected */ }
-    assertFalse(mem.isAlive());
+    if (mem != null) { assertFalse(mem.isAlive()); }
     if (mem2 != null) { assertFalse(mem2.isAlive()); }
   }
 

src/test/java/org/apache/datasketches/memory/internal/AllocateDirectMemoryTest.java

@@ -51,7 +51,7 @@ public void simpleAllocateDirect() {
       assertTrue(wMem.isAlive());
     }
     //The TWR block has exited, so the memory should be not alive
-    assertFalse(wMem2.isAlive());
+    if (wMem2 != null) { assertFalse(wMem2.isAlive()); }
   }
 
   @Test