test: Enhance coverage for deprecated writeProperty method

Added comprehensive test coverage including:
- Null value handling
- Method chaining scenarios
- Multiple sequential writes

This improves test coverage for the restored deprecated writeProperty
method to meet Sonar quality gate requirements (80% coverage threshold).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: cuioss-oliver

src/test/java/de/cuioss/tools/property/PropertyUtilTest.java

@@ -140,6 +140,20 @@ void shouldSupportDeprecatedWriteProperty() {
         assertAll("Testing deprecated writeProperty",
                 () -> assertSame(underTest, result, "Should return the same bean instance for chaining"),
                 () -> assertEquals(number, readProperty(underTest, ATTRIBUTE_READ_WRITE), "Property value should be set correctly"));
+
+        // Test with null value
+        Object nullResult = writeProperty(underTest, ATTRIBUTE_READ_WRITE, null);
+        assertAll("Testing deprecated writeProperty with null",
+                () -> assertSame(underTest, nullResult, "Should return the bean instance even with null value"),
+                () -> assertNull(readProperty(underTest, ATTRIBUTE_READ_WRITE), "Property value should be null"));
+
+        // Test chaining multiple writes
+        Object chainResult = writeProperty(
+                writeProperty(underTest, ATTRIBUTE_READ_WRITE, 10),
+                ATTRIBUTE_READ_WRITE, 20);
+        assertAll("Testing method chaining",
+                () -> assertSame(underTest, chainResult, "Should return the bean for chaining"),
+                () -> assertEquals(20, readProperty(underTest, ATTRIBUTE_READ_WRITE), "Final value should be 20"));
     }
 
 }