diff --git a/dd-java-agent/agent-debugger/debugger-bootstrap/src/main/java/datadog/trace/bootstrap/debugger/util/WellKnownClasses.java b/dd-java-agent/agent-debugger/debugger-bootstrap/src/main/java/datadog/trace/bootstrap/debugger/util/WellKnownClasses.java
index 7512d1b0212..5c5b91cd66d 100644
--- a/dd-java-agent/agent-debugger/debugger-bootstrap/src/main/java/datadog/trace/bootstrap/debugger/util/WellKnownClasses.java
+++ b/dd-java-agent/agent-debugger/debugger-bootstrap/src/main/java/datadog/trace/bootstrap/debugger/util/WellKnownClasses.java
@@ -107,6 +107,7 @@ public class WellKnownClasses {
               "java.time.LocalDate",
               "java.time.LocalDateTime",
               "java.util.UUID",
+              "java.net.URI",
               "java.io.File",
               "sun.nio.fs.UnixPath",
               "sun.nio.fs.WindowsPath"));
diff --git a/dd-java-agent/agent-debugger/debugger-el/src/main/java/com/datadog/debugger/el/expressions/SubStringExpression.java b/dd-java-agent/agent-debugger/debugger-el/src/main/java/com/datadog/debugger/el/expressions/SubStringExpression.java
index 1c566a5591e..9788fc977ee 100644
--- a/dd-java-agent/agent-debugger/debugger-el/src/main/java/com/datadog/debugger/el/expressions/SubStringExpression.java
+++ b/dd-java-agent/agent-debugger/debugger-el/src/main/java/com/datadog/debugger/el/expressions/SubStringExpression.java
@@ -20,17 +20,29 @@ public SubStringExpression(ValueExpression<?> source, int startIndex, int endInd
   @Override
   public Value<String> evaluate(ValueReferenceResolver valueRefResolver) {
     Value<?> sourceValue = source != null ? source.evaluate(valueRefResolver) : Value.nullValue();
+    if (sourceValue.isUndefined()) {
+      throw new EvaluationException(
+          "Cannot evaluate the expression for undefined value", PrettyPrintVisitor.print(this));
+    }
+    if (sourceValue.isNull()) {
+      throw new EvaluationException(
+          "Cannot evaluate the expression for null value", PrettyPrintVisitor.print(this));
+    }
     if (sourceValue.getValue() instanceof String) {
       String sourceStr = (String) sourceValue.getValue();
-      try {
-        return (Value<String>) Value.of(sourceStr.substring(startIndex, endIndex));
-      } catch (StringIndexOutOfBoundsException ex) {
-        throw new EvaluationException(ex.getMessage(), PrettyPrintVisitor.print(this), ex);
-      }
+      return internalEvaluate(sourceStr);
     }
     return Value.undefined();
   }
 
+  private Value<String> internalEvaluate(String sourceStr) {
+    try {
+      return (Value<String>) Value.of(sourceStr.substring(startIndex, endIndex));
+    } catch (StringIndexOutOfBoundsException ex) {
+      throw new EvaluationException(ex.getMessage(), PrettyPrintVisitor.print(this), ex);
+    }
+  }
+
   @Override
   public <R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
diff --git a/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/EndsWithExpressionTest.java b/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/EndsWithExpressionTest.java
index 2b4c74a3752..17a6b1c07f1 100644
--- a/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/EndsWithExpressionTest.java
+++ b/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/EndsWithExpressionTest.java
@@ -12,10 +12,13 @@
 import com.datadog.debugger.el.values.StringValue;
 import datadog.trace.bootstrap.debugger.el.ValueReferenceResolver;
 import datadog.trace.bootstrap.debugger.el.Values;
+import java.net.URI;
 import org.junit.jupiter.api.Test;
 
 class EndsWithExpressionTest {
   private final ValueReferenceResolver resolver = RefResolverHelper.createResolver(this);
+  // used to ref lookup
+  URI uri = URI.create("https://www.datadoghq.com");
 
   @Test
   void nullExpression() {
@@ -46,4 +49,11 @@ void stringExpression() {
     assertFalse(expression.evaluate(resolver));
     assertEquals("endsWith(\"abc\", \"ab\")", print(expression));
   }
+
+  @Test
+  void stringPrimitives() {
+    EndsWithExpression expression = new EndsWithExpression(DSL.ref("uri"), new StringValue(".com"));
+    assertTrue(expression.evaluate(resolver));
+    assertEquals("endsWith(uri, \".com\")", print(expression));
+  }
 }
diff --git a/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/MatchesExpressionTest.java b/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/MatchesExpressionTest.java
index b4afe7e1a10..23cfc0c7c66 100644
--- a/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/MatchesExpressionTest.java
+++ b/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/MatchesExpressionTest.java
@@ -9,10 +9,13 @@
 import com.datadog.debugger.el.values.StringValue;
 import datadog.trace.bootstrap.debugger.el.ValueReferenceResolver;
 import datadog.trace.bootstrap.debugger.el.Values;
+import java.net.URI;
 import org.junit.jupiter.api.Test;
 
 class MatchesExpressionTest {
   private final ValueReferenceResolver resolver = RefResolverHelper.createResolver(this);
+  // used to ref lookup
+  URI uri = URI.create("https://www.datadoghq.com");
 
   @Test
   void nullExpression() {
@@ -49,4 +52,12 @@ void stringExpression() {
     assertFalse(expression.evaluate(resolver));
     assertEquals("matches(\"abc\", \"[def]+\")", print(expression));
   }
+
+  @Test
+  void stringPrimitives() {
+    MatchesExpression expression =
+        new MatchesExpression(DSL.ref("uri"), new StringValue("^https?://w{3}\\.datadoghq\\.com$"));
+    assertTrue(expression.evaluate(resolver));
+    assertEquals("matches(uri, \"^https?://w{3}\\.datadoghq\\.com$\")", print(expression));
+  }
 }
diff --git a/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/StartsWithExpressionTest.java b/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/StartsWithExpressionTest.java
index 7c9a2347afb..0626dc1d6ff 100644
--- a/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/StartsWithExpressionTest.java
+++ b/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/StartsWithExpressionTest.java
@@ -9,10 +9,13 @@
 import com.datadog.debugger.el.values.StringValue;
 import datadog.trace.bootstrap.debugger.el.ValueReferenceResolver;
 import datadog.trace.bootstrap.debugger.el.Values;
+import java.net.URI;
 import org.junit.jupiter.api.Test;
 
 class StartsWithExpressionTest {
   private final ValueReferenceResolver resolver = RefResolverHelper.createResolver(this);
+  // used to ref lookup
+  URI uri = URI.create("https://www.datadoghq.com");
 
   @Test
   void nullExpression() {
@@ -44,4 +47,12 @@ void stringExpression() {
     assertFalse(expression.evaluate(resolver));
     assertEquals("startsWith(\"abc\", \"bc\")", print(expression));
   }
+
+  @Test
+  void stringPrimitives() {
+    StartsWithExpression expression =
+        new StartsWithExpression(DSL.ref("uri"), new StringValue("https"));
+    assertTrue(expression.evaluate(resolver));
+    assertEquals("startsWith(uri, \"https\")", print(expression));
+  }
 }
diff --git a/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/SubStringExpressionTest.java b/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/SubStringExpressionTest.java
index bcaaa730974..57c2ddb8291 100644
--- a/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/SubStringExpressionTest.java
+++ b/dd-java-agent/agent-debugger/debugger-el/src/test/java/com/datadog/debugger/el/expressions/SubStringExpressionTest.java
@@ -3,31 +3,40 @@
 import static com.datadog.debugger.el.PrettyPrintVisitor.print;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.datadog.debugger.el.DSL;
 import com.datadog.debugger.el.EvaluationException;
 import com.datadog.debugger.el.RefResolverHelper;
 import datadog.trace.bootstrap.debugger.el.ValueReferenceResolver;
 import datadog.trace.bootstrap.debugger.el.Values;
+import java.net.URI;
 import org.junit.jupiter.api.Test;
 
 public class SubStringExpressionTest {
   private final ValueReferenceResolver resolver = RefResolverHelper.createResolver(this);
+  // used to ref lookup
+  URI uri = URI.create("https://www.datadoghq.com");
+  Object nullValue = null;
 
   @Test
   void nullExpression() {
-    SubStringExpression expression = new SubStringExpression(null, 0, 0);
-    assertTrue(expression.evaluate(resolver).isUndefined());
-    assertEquals("substring(null, 0, 0)", print(expression));
+    SubStringExpression expression1 = new SubStringExpression(null, 0, 0);
+    EvaluationException evaluationException =
+        assertThrows(EvaluationException.class, () -> expression1.evaluate(resolver));
+    assertEquals("substring(null, 0, 0)", evaluationException.getExpr());
+    SubStringExpression expression2 = new SubStringExpression(DSL.ref("nullValue"), 0, 0);
+    evaluationException =
+        assertThrows(EvaluationException.class, () -> expression2.evaluate(resolver));
+    assertEquals("substring(nullValue, 0, 0)", evaluationException.getExpr());
   }
 
   @Test
   void undefinedExpression() {
     SubStringExpression expression =
         new SubStringExpression(DSL.value(Values.UNDEFINED_OBJECT), 0, 0);
-    assertTrue(expression.evaluate(resolver).isUndefined());
-    assertEquals("substring(UNDEFINED, 0, 0)", print(expression));
+    EvaluationException evaluationException =
+        assertThrows(EvaluationException.class, () -> expression.evaluate(resolver));
+    assertEquals("substring(UNDEFINED, 0, 0)", evaluationException.getExpr());
   }
 
   @Test
@@ -44,4 +53,11 @@ void stringOutOfBoundsExpression() {
         assertThrows(EvaluationException.class, () -> expression.evaluate(resolver));
     assertEquals("substring(\"abc\", 0, 10)", evaluationException.getExpr());
   }
+
+  @Test
+  void stringPrimitives() {
+    SubStringExpression expression = new SubStringExpression(DSL.ref("uri"), 0, 5);
+    assertEquals("https", expression.evaluate(resolver).getValue());
+    assertEquals("substring(uri, 0, 5)", print(expression));
+  }
 }