chore: use jspecify annotations for Nullable

Author: nielm

pom.xml

@@ -41,6 +41,7 @@
     <error-prone.version>2.36.0</error-prone.version>
     <maven-checkstyle-plugin.version>3.6.0</maven-checkstyle-plugin.version>
     <maven-assembly-plugin.version>3.7.1</maven-assembly-plugin.version>
+    <jspecify.version>1.0.0</jspecify.version>
   </properties>
   <dependencies>
     <dependency>
@@ -86,6 +87,11 @@
         </exclusion>
       </exclusions>
     </dependency>
+    <dependency>
+      <groupId>org.jspecify</groupId>
+      <artifactId>jspecify</artifactId>
+      <version> ${jspecify.version}</version>
+    </dependency>
   </dependencies>
   <build>
     <pluginManagement>

src/main/java/com/google/cloud/solutions/spannerddl/parser/ASTcolumn_def.java

@@ -18,7 +18,7 @@
 
 import com.google.cloud.solutions.spannerddl.diff.AstTreeUtils;
 import com.google.common.base.Joiner;
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class ASTcolumn_def extends SimpleNode {