Create rule S8315: Empty strings should not be used for type conversion

rules/S8315/groovy/metadata.json

@@ -0,0 +1,25 @@
+{
+  "title": "Empty strings should not be used for type conversion",
+  "type": "CODE_SMELL",
+  "status": "beta",
+  "remediation": {
+    "func": "Constant/Issue",
+    "constantCost": "5 min"
+  },
+  "tags": [
+  ],
+  "defaultSeverity": "Major",
+  "ruleSpecification": "RSPEC-8315",
+  "sqKey": "S8315",
+  "scope": "Main",
+  "defaultQualityProfiles": [
+    "Sonar way"
+  ],
+  "quickfix": "unknown",
+  "code": {
+    "impacts": {
+      "MAINTAINABILITY": "HIGH"
+    },
+    "attribute": "EFFICIENT"
+  }
+}

rules/S8315/groovy/rule.adoc

@@ -0,0 +1,44 @@
+This rule raises an issue when an empty string literal is concatenated with another value using the `+` operator.
+
+== Why is this an issue?
+
+Concatenating an empty string with another value is an inefficient way to convert that value to a string. This pattern creates unnecessary string objects and obscures the developer's intent.
+
+In Groovy, when you use `'' + someValue`, the runtime must:
+
+* Create a new empty string object
+* Convert `someValue` to a string representation
+* Concatenate the empty string with the converted value
+* Return the result
+
+This approach is less efficient than direct string conversion methods and makes the code less readable. The intent (converting a value to a string) is not immediately clear to other developers reading the code.
+
+Moreover, this pattern can lead to unexpected behavior with null values, as `'' + null` results in the string `"null"` rather than an empty string or a null pointer exception that might be more appropriate depending on the context.
+
+== How to fix it
+
+Replace empty string concatenation with explicit `toString()` calls. For potentially null values, use safe navigation with null coalescing to handle null cases appropriately.
+
+=== Code examples
+
+==== Noncompliant code example
+
+[source,groovy,diff-id=1,diff-type=noncompliant]
+----
+def variable = method('' + property)
+----
+
+==== Compliant solution
+
+[source,groovy,diff-id=1,diff-type=compliant]
+----
+def variable = method(property?.toString() ?: "")
+----
+
+== Resources
+
+=== Documentation
+
+ * Groovy documentation - https://groovy-lang.org/syntax.html#_string_summary_table[String handling and conversion methods]
+
+ * Groovy documentation - https://groovy-lang.org/operators.html#_safe_navigation_operator[Safe navigation operator]

rules/S8315/metadata.json

@@ -0,0 +1,2 @@
+{
+}