Add a null check for oas path in tool integration

Author: TharmiganK

openapi-bal-task-plugin/src/main/java/io/ballerina/openapi/bal/tool/Constants.java

@@ -71,7 +71,8 @@ public enum DiagnosticMessages {
         ERROR_WHILE_UPDATING_TOML("OAS_CLIENT_11", "error occurred when updating Ballerina.toml " +
                 "file with the client native dependency.", DiagnosticSeverity.ERROR),
         OPENAPI_EXCEPTION("OAS_CLIENT_12", "exception occurred while reading the openapi contract: %s",
-                DiagnosticSeverity.ERROR);
+                DiagnosticSeverity.ERROR),
+        CONTRACT_PATH_NOT_PROVIDED("OAS_CLIENT_13", "OpenAPI file path is not provided.", DiagnosticSeverity.ERROR);
 
         private final String code;
         private final String description;

openapi-bal-task-plugin/src/main/java/io/ballerina/openapi/bal/tool/OpenAPICodeGeneratorTool.java

@@ -113,8 +113,19 @@ public void execute(ToolContext toolContext) {
         ImmutablePair<OASClientConfig, OASServiceMetadata> codeGeneratorConfig;
         TomlNodeLocation location = toolContext.currentPackage().ballerinaToml().get().tomlAstNode().location();
         try {
+            // Check the file path
+            String oasPath = toolContext.filePath();
+            if (Objects.isNull(oasPath)) {
+                DiagnosticMessages error = DiagnosticMessages.CONTRACT_PATH_NOT_PROVIDED;
+                createDiagnostics(toolContext, error, location);
+                return;
+            }
+            if (oasPath.isBlank()) {
+                DiagnosticMessages error = DiagnosticMessages.EMPTY_CONTRACT_PATH;
+                createDiagnostics(toolContext, error, location);
+            }
             // Validate the OAS file whether we can handle within OpenAPI tool
-            if (!canHandle(toolContext)) {
+            if (!canHandle(oasPath)) {
                 DiagnosticMessages error = DiagnosticMessages.WARNING_FOR_UNSUPPORTED_CONTRACT;
                 createDiagnostics(toolContext, error, location);
                 return;
@@ -199,14 +210,7 @@ private void handleCodeGenerationMode(ToolContext toolContext,
      * This method uses to check whether given specification can be handled via the openapi client generation tool.
      * This includes basic requirements like file extension check.
      */
-    private boolean canHandle(ToolContext toolContext) {
-        String oasPath = toolContext.filePath();
-        if (oasPath.isBlank()) {
-            TomlNodeLocation location = toolContext.currentPackage().ballerinaToml().get().tomlAstNode().location();
-            DiagnosticMessages error = DiagnosticMessages.EMPTY_CONTRACT_PATH;
-            createDiagnostics(toolContext, error, location);
-            return false;
-        }
+    private boolean canHandle(String oasPath) {
         return (oasPath.endsWith(YAML_EXTENSION) || oasPath.endsWith(JSON_EXTENSION) ||
                 oasPath.endsWith(YML_EXTENSION));
     }