Minor: Rename StringUtils#isEmpty to #isBlank

- Better fits the naming used by other tools and also the JDK (String#isBlank as of JDK 11)

src/test/java/fr/xephi/authme/command/CommandInitializerTest.java

@@ -138,11 +138,11 @@ public class CommandInitializerTest {
                 String forCommandText = " for command with labels '" + command.getLabels() + "'";
 
                 assertThat("has description" + forCommandText,
-                    StringUtils.isEmpty(command.getDescription()), equalTo(false));
+                    StringUtils.isBlank(command.getDescription()), equalTo(false));
                 assertThat("short description doesn't end in '.'" + forCommandText,
                     command.getDescription().endsWith("."), equalTo(false));
                 assertThat("has detailed description" + forCommandText,
-                    StringUtils.isEmpty(command.getDetailedDescription()), equalTo(false));
+                    StringUtils.isBlank(command.getDetailedDescription()), equalTo(false));
                 assertThat("detailed description ends in '.'" + forCommandText,
                     command.getDetailedDescription().endsWith("."), equalTo(true));
             }

src/test/java/fr/xephi/authme/command/executable/authme/ConverterCommandTest.java

@@ -93,7 +93,7 @@ public class ConverterCommandTest {
         // when / then
         for (Map.Entry<String, Class<? extends Converter>> entry : ConverterCommand.CONVERTERS.entrySet()) {
             assertThat("Name is not null or empty",
-                StringUtils.isEmpty(entry.getKey()), equalTo(false));
+                StringUtils.isBlank(entry.getKey()), equalTo(false));
 
             assertThat("Converter class is unique for each entry",
                 classes.add(entry.getValue()), equalTo(true));

src/test/java/fr/xephi/authme/command/help/HelpMessageAndHelpSectionConsistencyTest.java

@@ -23,14 +23,14 @@ public class HelpMessageAndHelpSectionConsistencyTest {
         // when / then
         for (HelpMessage message : HelpMessage.values()) {
             assertThat("Key for message '" + message + "' is empty",
-                StringUtils.isEmpty(message.getKey()), equalTo(false));
+                StringUtils.isBlank(message.getKey()), equalTo(false));
             if (!keys.add(message.getKey())) {
                 fail("Key for message '" + message + "' is already used elsewhere");
             }
         }
         for (HelpSection section : HelpSection.values()) {
             assertThat("Key for section '" + section + "' is empty",
-                StringUtils.isEmpty(section.getKey()), equalTo(false));
+                StringUtils.isBlank(section.getKey()), equalTo(false));
             if (!keys.add(section.getKey())) {
                 fail("Key for section '" + section + "' is already used elsewhere");
             }

src/test/java/fr/xephi/authme/message/MessageKeyTest.java

@@ -27,7 +27,7 @@ public class MessageKeyTest {
             String key = messageKey.getKey();
             if (!keys.add(key)) {
                 fail("Found key '" + messageKey.getKey() + "' twice!");
-            } else if (StringUtils.isEmpty(key)) {
+            } else if (StringUtils.isBlank(key)) {
                 fail("Key for message key '" + messageKey + "' is empty");
             }
         }

src/test/java/fr/xephi/authme/message/MessagesFileConsistencyTest.java

@@ -40,7 +40,7 @@ public class MessagesFileConsistencyTest {
         final String key = messageKey.getKey();
         final String message = reader.getString(key);
 
-        if (StringUtils.isEmpty(message)) {
+        if (StringUtils.isBlank(message)) {
             errors.add("Messages file should have message for key '" + key + "'");
             return;
         }

src/test/java/fr/xephi/authme/message/YamlTextFileCheckerTest.java

@@ -81,7 +81,7 @@ public class YamlTextFileCheckerTest {
     private void checkFile(File file, String mandatoryKey, List<String> errors) {
         try {
             PropertyReader reader = new YamlFileReader(file);
-            if (StringUtils.isEmpty(reader.getString(mandatoryKey))) {
+            if (StringUtils.isBlank(reader.getString(mandatoryKey))) {
                 errors.add("Message for '" + mandatoryKey + "' is empty");
             }
         } catch (Exception e) {

src/test/java/fr/xephi/authme/security/HashAlgorithmIntegrationTest.java

@@ -74,9 +74,9 @@ public class HashAlgorithmIntegrationTest {
                 }
                 HashedPassword hashedPassword = method.computeHash("pwd", "name");
                 assertThat("Salt should not be null if method.hasSeparateSalt(), and vice versa. Method: '"
-                    + method + "'", StringUtils.isEmpty(hashedPassword.getSalt()), equalTo(!method.hasSeparateSalt()));
+                    + method + "'", StringUtils.isBlank(hashedPassword.getSalt()), equalTo(!method.hasSeparateSalt()));
                 assertThat("Hash should not be empty for method '" + method + "'",
-                    StringUtils.isEmpty(hashedPassword.getHash()), equalTo(false));
+                    StringUtils.isBlank(hashedPassword.getHash()), equalTo(false));
             }
         }
     }

src/test/java/fr/xephi/authme/util/StringUtilsTest.java

@@ -49,15 +49,15 @@ public class StringUtilsTest {
     }
 
     @Test
-    public void shouldCheckIsEmptyUtil() {
+    public void shouldCheckIfIsBlankString() {
         // Should be true for null/empty/whitespace
-        assertTrue(StringUtils.isEmpty(null));
-        assertTrue(StringUtils.isEmpty(""));
-        assertTrue(StringUtils.isEmpty(" \t"));
+        assertTrue(StringUtils.isBlank(null));
+        assertTrue(StringUtils.isBlank(""));
+        assertTrue(StringUtils.isBlank(" \t"));
 
         // Should be false if string has content
-        assertFalse(StringUtils.isEmpty("P"));
-        assertFalse(StringUtils.isEmpty(" test"));
+        assertFalse(StringUtils.isBlank("P"));
+        assertFalse(StringUtils.isBlank(" test"));
     }
 
     @Test