Address comments

Signed-off-by: Srikanth Govindarajan <srigovs@amazon.com>

data-prepper-pipeline-parser/src/main/java/org/opensearch/dataprepper/pipeline/parser/rule/RuleEvaluator.java

@@ -35,6 +35,7 @@ public class RuleEvaluator {
     private static final ObjectMapper yamlMapper = new ObjectMapper(new YAMLFactory());
     private final TransformersFactory transformersFactory;
 
+
     public RuleEvaluator(TransformersFactory transformersFactory) {
         this.transformersFactory = transformersFactory;
     }
@@ -63,9 +64,6 @@ public RuleEvaluatorResult isTransformationNeeded(PipelinesDataFlowModel pipelin
                             .withPipelineName(entry.getKey())
                             .build();
                 }
-            } catch (FileNotFoundException e) {
-                LOG.error("Template File Not Found");
-                throw new RuntimeException(e);
             } catch (JsonProcessingException e) {
                 LOG.error("Error processing json");
                 throw new RuntimeException(e);
@@ -128,7 +126,7 @@ private RuleFileEvaluation evaluate(String pipelinesJson) {
             }
 
         } catch (FileNotFoundException e) {
-            LOG.debug("Rule File Not Found");
+            LOG.debug("Rule File Not Found", e);
             return RuleFileEvaluation.builder()
                     .withPluginName(null)
                     .withRuleFileName(null)

data-prepper-plugins/dummy-plugin/README.md

@@ -0,0 +1,63 @@
+A dummy plugin is used specifically when we want to use pipeline transformation for a 
+plugin that does not exist.
+
+We can define a rule and template for this plugin by creating a plugin folder and
+place rule for which the pipeline configuration would be valid and a corresponding
+template to transform to when the rule is valid.
+
+For further details on transformation refer:
+/docs/pipeline_configuration_transformation.md
+
+
+For Example:
+
+User Config:
+```yaml
+test-pipeline:
+  source:
+    file:
+      path: "/full/path/to/logs_json.log"
+      record_type: "event"
+      format: "json"
+  processor:
+    - dummy_plugin:
+  sink:
+    - stdout:
+```
+
+Here dummy_plugin is not really a plugin that is defined in dataprepper, but we can 
+use the pipeline transformation to convert the user-config to different config based 
+on the template.
+
+Rule:
+```yaml
+plugin_name: "dummy-plugin"
+apply_when:
+  - "$.test-pipeline.processor[?(@.dummy_plugin)]"
+```
+
+Template:
+```yaml
+test-pipeline:
+  source:
+    file:
+      path: "/tmp/input-file.log"
+  processor:
+    - string_converter:
+        upper_case: true
+  sink:
+    - noop:
+```
+
+Output:
+```yaml
+test-pipeline:
+  source:
+    file:
+      path: "/tmp/input-file.log"
+  processor:
+    - string_converter:
+        upper_case: true
+  sink:
+    - noop:
+```