diff --git a/src/net/sourceforge/plantuml/StringUtils.java b/src/net/sourceforge/plantuml/StringUtils.java
index 4db4f0331..50dafe0aa 100644
--- a/src/net/sourceforge/plantuml/StringUtils.java
+++ b/src/net/sourceforge/plantuml/StringUtils.java
@@ -5,12 +5,12 @@
  * (C) Copyright 2009-2020, Arnaud Roques
  *
  * Project Info:  http://plantuml.com
- * 
+ *
  * If you like this project or if you find it useful, you can support us at:
- * 
+ *
  * http://plantuml.com/patreon (only 1$ per month!)
  * http://plantuml.com/paypal
- * 
+ *
  * This file is part of PlantUML.
  *
  * PlantUML is free software; you can redistribute it and/or modify it
@@ -119,16 +119,22 @@ public class StringUtils {
 		return result;
 	}
 
-	public static boolean isNotEmpty(String input) {
-		return input != null && trin(input).length() > 0;
+	public static boolean isNotEmpty(CharSequence s) {
+		return !isEmpty(s);
 	}
 
 	public static boolean isNotEmpty(List<? extends CharSequence> input) {
 		return input != null && input.size() > 0;
 	}
 
-	public static boolean isEmpty(String input) {
-		return input == null || trin(input).length() == 0;
+	public static boolean isEmpty(CharSequence s) {
+		if (s == null) return true;
+		final int length = s.length();
+		if (length == 0) return true;
+		for (int i = 0; i < length; i++) {
+			if (!isSpaceOrTabOrNull(s.charAt(i))) return false;
+		}
+		return true;
 	}
 
 	public static String manageHtml(String s) {
diff --git a/test/net/sourceforge/plantuml/StringUtilsTest.java b/test/net/sourceforge/plantuml/StringUtilsTest.java
new file mode 100644
index 000000000..39c9f3600
--- /dev/null
+++ b/test/net/sourceforge/plantuml/StringUtilsTest.java
@@ -0,0 +1,29 @@
+package net.sourceforge.plantuml;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+class StringUtilsTest {
+
+	@ParameterizedTest
+	@CsvSource(nullValues = "null", value = {
+			" null   , true  ",
+			" ''     , true  ",
+			" ' '    , true  ",
+			" '\0'   , true  ",
+			" '\n'   , true  ",
+			" '\r'   , true  ",
+			" '\t'   , true  ",
+			" 'x'    , false ",
+			" ' x '  , false ",
+	})
+	void test_isEmpty_isNotEmpty(String s, boolean empty) {
+		assertThat(StringUtils.isEmpty(s))
+				.isEqualTo(empty);
+
+		assertThat(StringUtils.isNotEmpty(s))
+				.isNotEqualTo(empty);
+	}
+}