diff --git a/src/__tests__/build.test.ts b/src/__tests__/build.test.ts
index e99f7dd..bad76b6 100644
--- a/src/__tests__/build.test.ts
+++ b/src/__tests__/build.test.ts
@@ -20,8 +20,16 @@ describe('build', () => {
       expect(build({ root: { item: ['a', 'b', 'c'] } })).toBe('<root><item>a</item><item>b</item><item>c</item></root>');
     });
 
-    it('builds empty string as self-closing tag', () => {
-      expect(build({ root: { empty: '' } })).toBe('<root><empty/></root>');
+    it('builds empty string as open/close tags', () => {
+      expect(build({ root: { empty: '' } })).toBe('<root><empty></empty></root>');
+    });
+
+    it('builds null as self-closing tag', () => {
+      expect(build({ root: { nullField: null, version: '1.0' } })).toBe('<root><nullField/><version>1.0</version></root>');
+    });
+
+    it('skips undefined values', () => {
+      expect(build({ root: { undef: undefined, kept: 'val' } })).toBe('<root><kept>val</kept></root>');
     });
 
     it('builds numeric values', () => {
diff --git a/src/__tests__/parse.test.ts b/src/__tests__/parse.test.ts
index bade996..55c83f3 100644
--- a/src/__tests__/parse.test.ts
+++ b/src/__tests__/parse.test.ts
@@ -57,7 +57,7 @@ describe('parse', () => {
   describe('attributes', () => {
     it('parses attributes with default prefix', () => {
       const result = parse('<root id="1" name="test">value</root>');
-      expect(result).toEqual({ root: { '#text': 'value', '@_id': 1, '@_name': 'test' } });
+      expect(result).toEqual({ root: { '#text': 'value', '@_id': '1', '@_name': 'test' } });
     });
 
     it('parses attributes on nested elements', () => {
@@ -67,7 +67,7 @@ describe('parse', () => {
 
     it('parses self-closing tag with attributes', () => {
       const result = parse('<root><item id="1"/></root>');
-      expect(result).toEqual({ root: { item: { '@_id': 1 } } });
+      expect(result).toEqual({ root: { item: { '@_id': '1' } } });
     });
 
     it('ignores attributes when ignoreAttributes is true', () => {
@@ -81,12 +81,12 @@ describe('parse', () => {
       const result = parse('<root id="1">text</root>', {
         attributeNamePrefix: '@',
       });
-      expect(result).toEqual({ root: { '#text': 'text', '@id': 1 } });
+      expect(result).toEqual({ root: { '#text': 'text', '@id': '1' } });
     });
 
     it('handles attributes with single quotes', () => {
       const result = parse("<root id='42'>text</root>");
-      expect(result).toEqual({ root: { '#text': 'text', '@_id': 42 } });
+      expect(result).toEqual({ root: { '#text': 'text', '@_id': '42' } });
     });
   });
 
@@ -105,8 +105,8 @@ describe('parse', () => {
       const result = parse('<root xmlns:sf="http://example.com" sf:id="1">text</root>', {
         removeNSPrefix: true,
       });
-      // xmlns:sf -> removeNS -> sf, sf:id -> removeNS -> id
-      expect(result).toEqual({ root: { '#text': 'text', '@_sf': 'http://example.com', '@_id': 1 } });
+      // xmlns:sf is stripped entirely, sf:id -> removeNS -> id
+      expect(result).toEqual({ root: { '#text': 'text', '@_id': '1' } });
     });
   });
 
@@ -346,9 +346,9 @@ describe('parse', () => {
       expect(execResult.success).toBe(true);
       expect(execResult.line).toBe(-1);
       // xsi:nil="true" self-closing tags have the nil attribute (ns-prefix stripped)
-      expect(execResult.compileProblem).toEqual({ '@_nil': true });
-      expect(execResult.exceptionMessage).toEqual({ '@_nil': true });
-      expect(execResult.exceptionStackTrace).toEqual({ '@_nil': true });
+      expect(execResult.compileProblem).toEqual({ '@_nil': 'true' });
+      expect(execResult.exceptionMessage).toEqual({ '@_nil': 'true' });
+      expect(execResult.exceptionStackTrace).toEqual({ '@_nil': 'true' });
     });
   });
 });
diff --git a/src/build.ts b/src/build.ts
index e3cc6d9..229e48f 100644
--- a/src/build.ts
+++ b/src/build.ts
@@ -23,7 +23,14 @@ export function build(obj: Record<string, unknown>, options?: BuildOptions): str
   const parts: string[] = [];
 
   function serialize(key: string, value: unknown, depth: number): void {
-    if (value === null || value === undefined) return;
+    if (value === undefined) return;
+
+    if (value === null) {
+      const indent = format ? indentBy.repeat(depth) : '';
+      const nl = format ? '\n' : '';
+      parts.push(`${indent}<${key}/>${nl}`);
+      return;
+    }
 
     const indent = format ? indentBy.repeat(depth) : '';
     const nl = format ? '\n' : '';
@@ -76,11 +83,7 @@ export function build(obj: Record<string, unknown>, options?: BuildOptions): str
     } else {
       // Primitive value
       const str = String(value);
-      if (str === '') {
-        parts.push(`${indent}<${key}/>${nl}`);
-      } else {
-        parts.push(`${indent}<${key}>${escapeXml(str)}</${key}>${nl}`);
-      }
+      parts.push(`${indent}<${key}>${escapeXml(str)}</${key}>${nl}`);
     }
   }
 
diff --git a/src/parse.ts b/src/parse.ts
index b0e749a..c75d5ed 100644
--- a/src/parse.ts
+++ b/src/parse.ts
@@ -260,10 +260,13 @@ function parseAttributes(
   const re = /([^\s=]+)\s*=\s*(?:"([^"]*)"|'([^']*)')/g;
   let match: RegExpExecArray | null;
   while ((match = re.exec(str)) !== null) {
-    let name = match[1]!;
+    const rawName = match[1]!;
     let value: string = (match[2] ?? match[3])!;
-    if (rmNS) name = removeNS(name);
+    // When stripping namespace prefixes, drop xmlns and xmlns:* declarations entirely
+    if (rmNS && (rawName === 'xmlns' || rawName.startsWith('xmlns:'))) continue;
+    const name = rmNS ? removeNS(rawName) : rawName;
     if (processEnt) value = decodeEntities(value);
-    attrs[prefix + name] = parseValue(value, coerce);
+    // Attribute values are always strings — never coerce
+    attrs[prefix + name] = value;
   }
 }