Add support for the Preconditions Class in the Guava framework

java/ql/src/semmle/code/java/frameworks/guava/Guava.qll

@@ -5,3 +5,4 @@
 import java
 import StringUtils
 import Collections
+import Preconditions

java/ql/src/semmle/code/java/frameworks/guava/Preconditions.qll

@@ -0,0 +1,23 @@
+/** Definitions of flow steps through the Preconditions class in the Guava framework. */
+
+import java
+private import semmle.code.java.dataflow.FlowSteps
+
+/**
+ * The class `com.google.common.base.Preconditions`.
+ */
+class TypeGuavaPreconditions extends Class {
+  TypeGuavaPreconditions() { this.hasQualifiedName("com.google.common.base", "Preconditions") }
+}
+
+/**
+ * A method that returns its argumnets.
+ */
+private class GuavaPreconditionsMethod extends TaintPreservingCallable {
+  GuavaPreconditionsMethod() {
+    this.getDeclaringType() instanceof TypeGuavaPreconditions and
+    this.hasName("checkNotNull")
+  }
+
+  override predicate returnsTaintFrom(int src) { src = 0 }
+}