String arguments should not be blank

README.md

@@ -15,7 +15,7 @@ To install, please refer to the [extensions documentation](https://github.com/ri
 To compile the source code located in `src/main/kotlin` and `src/test/kotlin` from the current project:
 
 ```java
-@BuildCommand(summary = "Compile the Kotlin project")
+@BuildCommand(summary = "Compiles the Kotlin project")
 public void compile() throws IOException {
     new CompileKotlinOperation()
             .fromProject(this)

examples/src/bld/java/com/example/ExampleBuild.java

@@ -32,8 +32,11 @@ public class ExampleBuild extends Project {
         autoDownloadPurge = true;
         repositories = List.of(MAVEN_LOCAL, MAVEN_CENTRAL, RIFE2_RELEASES);
 
+        final var kotlin = version(1, 9, 21);
         scope(compile)
-                .include(dependency("org.jetbrains.kotlin", "kotlin-stdlib", version(1, 9, 21)));
+                .include(dependency("org.jetbrains.kotlin", "kotlin-stdlib", kotlin))
+                .include(dependency("org.jetbrains.kotlin", "kotlin-stdlib-jdk7", kotlin))
+                .include(dependency("org.jetbrains.kotlin", "kotlin-stdlib-jdk8", kotlin));
         scope(test)
                 .include(dependency("org.jetbrains.kotlin:kotlin-test-junit5:1.9.21"))
                 .include(dependency("org.junit.jupiter", "junit-jupiter", version(5, 10, 1)))
@@ -57,7 +60,7 @@ public class ExampleBuild extends Project {
         new ExampleBuild().start(args);
     }
 
-    @BuildCommand(summary = "Compile the Kotlin project")
+    @BuildCommand(summary = "Compiles the Kotlin project")
     @Override
     public void compile() throws IOException {
         // The source code located in src/main/kotlin and src/test/kotlin will be compiled

src/main/java/rife/bld/extension/CompileKotlinOperation.java

@@ -94,6 +94,16 @@ public class CompileKotlinOperation extends AbstractOperation<CompileKotlinOpera
         }
     }
 
+    /**
+     * Determines if the given string is not blank.
+     *
+     * @param s the string
+     * @return {@code true} if not blank, {@code false} otherwise.
+     */
+    public static boolean isNotBlank(String s) {
+        return s != null && !s.isBlank();
+    }
+
     /**
      * Provides the main build destination directory.
      *
@@ -276,7 +286,7 @@ public class CompileKotlinOperation extends AbstractOperation<CompileKotlinOpera
         args.add(destination.getAbsolutePath());
 
         // friend-path
-        if (friendPaths != null) {
+        if (friendPaths != null && friendPaths.exists()) {
             args.add("-Xfriend-paths=" + friendPaths.getAbsolutePath());
         }
 

src/main/java/rife/bld/extension/CompileKotlinOptions.java

@@ -21,6 +21,8 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 
+import static rife.bld.extension.CompileKotlinOperation.isNotBlank;
+
 /**
  * Configuration for the Kotlin compiler options.
  *
@@ -106,8 +108,8 @@ public class CompileKotlinOptions {
     public List<String> args() {
         var args = new ArrayList<String>();
         
-        // api-version
+        // api-isNotBlankversion
-        if (apiVersion_ != null) {
+        if (isNotBlank(apiVersion_)) {
             args.add("-api-version");
             args.add(apiVersion_);
         }
@@ -129,7 +131,7 @@ public class CompileKotlinOptions {
         }
 
         // jvm-target
-        if (jvmTarget_ != null) {
+        if (isNotBlank(jvmTarget_)) {
             args.add("-jvm-target");
             args.add(jvmTarget_);
         }
@@ -140,30 +142,30 @@ public class CompileKotlinOptions {
         }
 
         // jdk-home
-        if (jdkHome_ != null) {
+        if (isNotBlank(jdkHome_)) {
             args.add("-jdk-home");
             args.add(jdkHome_);
         }
 
         // jdk-release
-        if (jdkRelease_ != null) {
+        if (isNotBlank(jdkRelease_)) {
             args.add("-Xjdk-release=" + jdkRelease_);
         }
 
         // kotlin-home
-        if (kotlinHome_ != null) {
+        if (isNotBlank(kotlinHome_)) {
             args.add("-kotlin-home");
             args.add(kotlinHome_);
         }
 
         // language-version
-        if (languageVersion_ != null) {
+        if (isNotBlank(languageVersion_)) {
             args.add("-language-version");
             args.add(languageVersion_);
         }
 
         // module-name
-        if (moduleName_ != null) {
+        if (isNotBlank(moduleName_)) {
             args.add("-module-name");
             args.add(moduleName_);
         }
@@ -202,7 +204,7 @@ public class CompileKotlinOptions {
         }
 
         // path
-        if (path_ != null) {
+        if (isNotBlank(path_)) {
             args.add("-d");
             args.add(path_);
         }

src/main/java/rife/bld/extension/dokka/DokkaOperation.java

@@ -27,6 +27,8 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
+import static rife.bld.extension.CompileKotlinOperation.isNotBlank;
+
 /**
  * Builds documentation (javadoc, HTML, etc.) using Dokka.
  *
@@ -172,13 +174,13 @@ public class DokkaOperation extends AbstractProcessOperation<DokkaOperation> {
         }
 
         // -moduleName
-        if (moduleName_ != null) {
+        if (isNotBlank(moduleName_)) {
             args.add("-moduleName");
             args.add(moduleName_);
         }
 
         // -moduleVersion
-        if (moduleVersion_ != null) {
+        if (isNotBlank(moduleVersion_)) {
             args.add("-moduleVersion");
             args.add(moduleVersion_);
         }