Addressed first batch of review comments

cpg-core/src/main/java/de/fraunhofer/aisec/cpg/graph/ArgumentHolder.kt

@@ -44,8 +44,14 @@ interface ArgumentHolder : Holder<Expression> {
     /** Adds the [expression] to the list of arguments. */
     fun addArgument(expression: Expression)
 
-    /** Removes the [expression] from the list of arguments. */
-    fun removeArgument(expression: Expression) {}
+    /**
+     * Removes the [expression] from the list of arguments.
+     *
+     * An indication whether this operation was successful needs to be returned.
+     */
+    fun removeArgument(expression: Expression): Boolean {
+        return false
+    }
 
     /**
      * Replaces the existing argument specified in [old] with the one in [new]. Implementation how

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/graph/HasInitializer.kt

@@ -31,22 +31,30 @@ import de.fraunhofer.aisec.cpg.graph.statements.expressions.Expression
  * Specifies that a certain node has an initializer. It is a special case of [ArgumentHolder], in
  * which the initializer is treated as the first (and only) argument.
  */
-interface HasInitializer : ArgumentHolder {
+interface HasInitializer : HasType, ArgumentHolder, AssignmentHolder {
 
     var initializer: Expression?
 
     override fun addArgument(expression: Expression) {
         this.initializer = expression
     }
 
-    override fun removeArgument(expression: Expression) {
-        if (this.initializer == expression) {
+    override fun removeArgument(expression: Expression): Boolean {
+        return if (this.initializer == expression) {
             this.initializer = null
+            true
+        } else {
+            false
         }
     }
 
     override fun replaceArgument(old: Expression, new: Expression): Boolean {
         this.initializer = new
         return true
     }
+
+    override val assignments: List<Assignment>
+        get() {
+            return initializer?.let { listOf(Assignment(it, this, this)) } ?: listOf()
+        }
 }

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/graph/declarations/VariableDeclaration.kt

@@ -33,8 +33,7 @@ import org.apache.commons.lang3.builder.ToStringBuilder
 import org.neo4j.ogm.annotation.Relationship
 
 /** Represents the declaration of a variable. */
-class VariableDeclaration :
-    ValueDeclaration(), HasType.TypeListener, HasInitializer, AssignmentHolder {
+class VariableDeclaration : ValueDeclaration(), HasType.TypeListener, HasInitializer {
 
     /**
      * We need a way to store the templateParameters that a VariableDeclaration might have before
@@ -129,11 +128,6 @@ class VariableDeclaration :
             .toString()
     }
 
-    override val assignments: List<Assignment>
-        get() {
-            return initializer?.let { listOf(Assignment(it, this, this)) } ?: listOf()
-        }
-
     override fun equals(other: Any?): Boolean {
         if (this === other) {
             return true

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/graph/statements/ReturnStatement.kt

@@ -60,8 +60,9 @@ class ReturnStatement : Statement(), ArgumentHolder {
         this.returnValues += expression
     }
 
-    override fun removeArgument(expression: Expression) {
+    override fun removeArgument(expression: Expression): Boolean {
         this.returnValues -= expression
+        return true
     }
 
     override fun replaceArgument(old: Expression, new: Expression): Boolean {

cpg-core/src/main/kotlin/de/fraunhofer/aisec/cpg/graph/statements/expressions/CallExpression.kt

@@ -148,8 +148,9 @@ open class CallExpression : Expression(), HasType.TypeListener, SecondaryTypeEdg
         return true
     }
 
-    override fun removeArgument(expression: Expression) {
+    override fun removeArgument(expression: Expression): Boolean {
         arguments -= expression
+        return true
     }
 
     /** Returns the function signature as list of types of the call arguments. */