feat: Issuer Optimizations

* Added Guava dependency to use in String checks etc.
* Added empty-null checks to Issuer (Person, Organization) properties

Refs: #4

pom.xml

@@ -14,18 +14,29 @@
         <dependency>
             <groupId>org.immutables</groupId>
             <artifactId>value</artifactId>
-            <version>2.8.8</version>
+            <version>2.9.2</version>
         </dependency>
         <dependency>
             <groupId>org.immutables</groupId>
             <artifactId>builder</artifactId>
-            <version>2.8.8</version>
+            <version>2.9.2</version>
         </dependency>
         <dependency>
             <groupId>jakarta.annotation</groupId>
             <artifactId>jakarta.annotation-api</artifactId>
             <version>2.1.1</version>
         </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <version>5.6.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.diffplug.guava</groupId>
+            <artifactId>guava-core</artifactId>
+            <version>19.0.0</version>
+        </dependency>
     </dependencies>
 
     <properties>

src/main/java/org/snturk/petition/Petition.java

@@ -12,41 +12,41 @@
 
 @Value.Immutable
 @Value.Style(strictBuilder = true)
-public abstract class Petition {
+public interface Petition {
 
     /**
      * By default id is generated by idGenerator function, but it can be overridden by setting id explicitly.
      * @return
      */
     @Value.Default
-    public @Nullable String id() {
-        return idGenerator().apply(this);
+    default @Nullable String getId() {
+        return getIdGenerator().apply(this);
     }
 
     /**
      * Name of the petition
      * @return
      */
-    public abstract String name();
+    String getName();
 
     /**
      * Title of the petition
      * @return
      */
-    public abstract String title();
+    String getTitle();
 
     /**
      * Issuer or signer of the petition
      * @return
      */
-    public abstract Issuer issuer();
+    Issuer getIssuer();
 
     /**
      * Date of the petition
      * @return
      */
     @Value.Default
-    public LocalDate issuedDate() {
+    default LocalDate getIssuedDate() {
         return LocalDate.now();
     }
 
@@ -55,17 +55,17 @@ public LocalDate issuedDate() {
      * @see PetitionType
      * @return PetitionType
      */
-    public abstract @Nullable PetitionType type();
+    @Nullable PetitionType getType();
 
     /**
      * Related attachments of the petition, key is the name of the attachment, value is the java.io.File object
      * @return
      */
-    public abstract @Nullable Map<String, File> attachments();
+    @Nullable Map<String, File> getAttachments();
 
     /**
      * Function to generate id of the petition
      * @return
      */
-    public abstract Function<Petition, String> idGenerator();
+    Function<Petition, String> getIdGenerator();
 }

src/main/java/org/snturk/petition/model/Organization.java

@@ -1,22 +1,35 @@
 package org.snturk.petition.model;
 
+import com.google.common.base.Strings;
+import org.snturk.petition.exceptions.InvalidIssuerException;
+
 public class Organization implements Issuer {
 
     private String corporateName;
     private String corporationType;
 
     public Organization(String corporateName) {
+        if (Strings.isNullOrEmpty(corporateName)) {
+            throw new InvalidIssuerException("Corporate name cannot be null or empty");
+        }
         this.corporateName = corporateName;
     }
 
     public Organization(String corporateName, String corporationType) {
+        if (Strings.isNullOrEmpty(corporateName)) {
+            throw new InvalidIssuerException("Corporate name cannot be null or empty");
+        }
+        if (Strings.isNullOrEmpty(corporationType)) {
+            throw new InvalidIssuerException("Corporation type cannot be null or empty, if there is no corporation type, use the other constructor");
+        }
         this.corporateName = corporateName;
         this.corporationType = corporationType;
     }
 
     @Override
     public String getCompleteName() {
-        return getCorporateName() + (getCorporationType().isEmpty() ? "" : " (" + getCorporationType() + ")");
+        String type = Strings.isNullOrEmpty(getCorporationType()) ? "" : " (" + getCorporationType() + ")";
+        return getCorporateName() + type;
     }
 
     public String getCorporateName() {

src/main/java/org/snturk/petition/model/Person.java

@@ -1,5 +1,6 @@
 package org.snturk.petition.model;
 
+import com.google.common.base.Strings;
 import org.snturk.petition.exceptions.InvalidIssuerException;
 
 public class Person implements Issuer {
@@ -11,25 +12,35 @@ public class Person implements Issuer {
     // TODO: Signature of the petition should be added here
 
     public Person(String firstName, String middleName, String lastName) {
-        if (firstName == null || firstName.isEmpty()) {
+        if (Strings.isNullOrEmpty(firstName)) {
             throw new InvalidIssuerException("First name cannot be null or empty");
         }
-        if (lastName == null || lastName.isEmpty()) {
+        if (Strings.isNullOrEmpty(lastName)) {
             throw new InvalidIssuerException("Last name cannot be null or empty");
         }
+        if (Strings.isNullOrEmpty(middleName)) {
+            throw new InvalidIssuerException("Middle name cannot be null or empty, if there is no middle name, use the other constructor");
+        }
         this.firstName = firstName;
         this.middleName = middleName;
         this.lastName = lastName;
     }
 
     public Person(String firstName, String lastName) {
+        if (Strings.isNullOrEmpty(firstName)) {
+            throw new InvalidIssuerException("First name cannot be null or empty");
+        }
+        if (Strings.isNullOrEmpty(lastName)) {
+            throw new InvalidIssuerException("Last name cannot be null or empty");
+        }
         this.firstName = firstName;
         this.lastName = lastName;
     }
 
     @Override
     public String getCompleteName() {
-        return getFirstName() + " " + (getMiddleName().isEmpty() ? "" : getMiddleName()) + " " + getLastName();
+        String middle = Strings.isNullOrEmpty(getMiddleName()) ? " " : " " + getMiddleName() + " ";
+        return getFirstName() + middle + getLastName();
     }
 
     public String getFirstName() {