title: Why is liquibase:diff returning "A reference database must be provided to perform a diff"?
body: <p>I ran "maven compile" successfully, but when I call "liquibase:diff" I get the following error. I am not sure this error corresponds to what the error actually is because I have clearly listed the database. I attached my pom.xml. I am new to liquibase and don't have much experience coding in a java environment. Thanks in advance for any assistance.</p>
  
  <blockquote>
    <p>Failed to execute goal org.liquibase:liquibase-maven-plugin:3.4.2:diff   > (default-cli) on project aerialrecon: A reference database must be       > provided to perform a diff. -> [Help 1]</p>
  </blockquote>
  
  <pre><code>         &lt;plugin&gt;
              &lt;groupId&gt;org.liquibase&lt;/groupId&gt;
              &lt;artifactId&gt;liquibase-maven-plugin&lt;/artifactId&gt;
              &lt;version&gt;${liquibase.version}&lt;/version&gt;
              &lt;configuration&gt;
                  &lt;changeLogFile&gt;src/main/resources/config/liquibase/master.xml&lt;/changeLogFile&gt;
                  &lt;diffChangeLogFile&gt;src/main/resources/config/liquibase/changelog/${maven.build.timestamp}_changelog.xml&lt;/diffChangeLogFile&gt;
                  &lt;driver&gt;com.mysql.jdbc.Driver&lt;/driver&gt;
                  &lt;url&gt;jdbc:mysql://us-cdbr-azure-northcentral-b.cloudapp.net&lt;/url&gt;
                  &lt;referencedatabaseref&gt;aerialrecon&lt;/referencedatabaseref&gt;
                  &lt;username&gt;username&lt;/username&gt;
                  &lt;password&gt;password&lt;/password&gt;
                  &lt;verbose&gt;true&lt;/verbose&gt;
                  &lt;logging&gt;debug&lt;/logging&gt;
              &lt;/configuration&gt;
              &lt;dependencies&gt;
                  &lt;dependency&gt;
                      &lt;groupId&gt;org.javassist&lt;/groupId&gt;
                      &lt;artifactId&gt;javassist&lt;/artifactId&gt;
                      &lt;version&gt;3.18.2-GA&lt;/version&gt;
                  &lt;/dependency&gt;
                  &lt;dependency&gt;
                      &lt;groupId&gt;org.liquibase.ext&lt;/groupId&gt;
                      &lt;artifactId&gt;liquibase-hibernate4&lt;/artifactId&gt;
                      &lt;version&gt;${liquibase-hibernate4.version}&lt;/version&gt;
                  &lt;/dependency&gt;
                  &lt;dependency&gt;
                      &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
                      &lt;artifactId&gt;spring-boot-starter-data-jpa&lt;/artifactId&gt;
                      &lt;version&gt;${project.parent.version}&lt;/version&gt;
                  &lt;/dependency&gt;
              &lt;/dependencies&gt;
          &lt;/plugin&gt;
  </code></pre>