Use String#isEmpty()

(build passes for me locally on Windows 10 and Linux
5.10.16.3-microsoft-standard-WSL2 #1 SMP Fri Apr 2 22:23:49 UTC 2021
x86_64 x86_64 x86_64 GNU/Linux (within Windows WSL)

Author: garydgregory

src/main/java/org/apache/commons/imaging/Imaging.java

@@ -760,12 +760,12 @@ public static ImageFormat guessFormat(final ByteSource byteSource) throws IOExce
                     .of(imageFormat.getExtensions())
                     .anyMatch(extension -> {
                         final String fileName = byteSource.getFileName();
-                        if (fileName == null || fileName.trim().length() == 0) {
+                        if (fileName == null || fileName.trim().isEmpty()) {
                             return false;
                         }
                         final String fileExtension = fileName.substring(fileName.lastIndexOf('.') + 1);
                         return extension != null
-                                && extension.trim().length() > 0
+                                && !extension.trim().isEmpty()
                                 && fileExtension.equalsIgnoreCase(extension);
                     }))
                 .findFirst()