Ensure null-safety for String uri and instance

Author: malczuuu

src/main/java/io/github/malczuuu/problem4j/core/ProblemBuilder.java

@@ -26,7 +26,6 @@ public interface ProblemBuilder {
    * @param type string URI identifying the problem type
    * @return this builder instance for chaining
    * @throws IllegalArgumentException if the string is not a valid URI
-   * @throws NullPointerException if the string is null
    */
   ProblemBuilder type(String type);
 
@@ -77,7 +76,6 @@ public interface ProblemBuilder {
    * @param instance string URI identifying the problem occurrence
    * @return this builder instance for chaining
    * @throws IllegalArgumentException if the string is not a valid URI
-   * @throws NullPointerException if the string is null
    */
   ProblemBuilder instance(String instance);
 

src/main/java/io/github/malczuuu/problem4j/core/ProblemBuilderImpl.java

@@ -27,7 +27,7 @@ public ProblemBuilder type(URI type) {
 
   @Override
   public ProblemBuilder type(String type) {
-    return type(URI.create(type));
+    return type != null ? type(URI.create(type)) : type((URI) null);
   }
 
   @Override
@@ -67,7 +67,7 @@ public ProblemBuilder instance(URI instance) {
 
   @Override
   public ProblemBuilder instance(String instance) {
-    return instance(URI.create(instance));
+    return instance != null ? instance(URI.create(instance)) : instance((URI) null);
   }
 
   @Override

src/test/java/io/github/malczuuu/problem4j/core/ProblemBuilderImplTests.java

@@ -2,6 +2,7 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import java.net.URI;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
@@ -10,6 +11,20 @@
 
 class ProblemBuilderImplTests {
 
+  @Test
+  void givenNullURIType_shouldNotSetIt() {
+    Problem problem = Problem.builder().type((URI) null).build();
+
+    assertThat(problem.getType()).isEqualTo(Problem.BLANK_TYPE);
+  }
+
+  @Test
+  void givenNullStringType_shouldNotSetIt() {
+    Problem problem = Problem.builder().type((String) null).build();
+
+    assertThat(problem.getType()).isEqualTo(Problem.BLANK_TYPE);
+  }
+
   @Test
   void givenNullProblemStatus_shouldNotSetTitleOrStatus() {
     Problem problem = Problem.builder().status(null).build();
@@ -18,6 +33,20 @@ void givenNullProblemStatus_shouldNotSetTitleOrStatus() {
     assertThat(problem.getTitle()).isNull();
   }
 
+  @Test
+  void givenNullURIInstance_shouldNotSetIt() {
+    Problem problem = Problem.builder().instance((URI) null).build();
+
+    assertThat(problem.getInstance()).isNull();
+  }
+
+  @Test
+  void givenNullStringInstance_shouldNotSetIt() {
+    Problem problem = Problem.builder().instance((String) null).build();
+
+    assertThat(problem.getInstance()).isNull();
+  }
+
   @Test
   void givenNullNameExtension_shouldIgnoreIt() {
     Problem problem = Problem.builder().extension(null, "value").build();