Collapsible "if" statements should be merged

Following the SonarQube:

Merging collapsible if statements increases the code's readability.

 
First case:

• GitHub: https://github.com/openmrs/openmrs-core/blob/master/api/src/main/java/liquibase/ext/sqlgenerator/core/ModifyColumnGenerator.java#L195-L200
• Sonar: https://sonar.openmrs.org/project/issues?id=org.openmrs%3Aopenmrs&issues=AXParDdh5zdzQEOFIPDa&open=AXParDdh5zdzQEOFIPDa

Second case:

• GitHub: https://github.com/openmrs/openmrs-core/blob/master/api/src/main/java/org/openmrs/util/MemoryAppender.java#L80-L87
• Sonar: https://sonar.openmrs.org/project/issues?id=org.openmrs%3Aopenmrs&issues=AXParDor5zdzQEOFIPEa&open=AXParDor5zdzQEOFIPEa

Third case:

• GitHub: https://github.com/openmrs/openmrs-core/blob/master/api/src/main/java/org/openmrs/util/ThreadSafeCircularFifoQueue.java#L759-L767
• Sonar: https://sonar.openmrs.org/project/issues?id=org.openmrs%3Aopenmrs&issues=AXParDpZ5zdzQEOFIPE8&open=AXParDpZ5zdzQEOFIPE8

Fourth case:

• GitHub: https://github.com/openmrs/openmrs-core/blob/master/api/src/main/java/org/openmrs/validator/UserValidator.java#L128-L132
• Sonar: https://sonar.openmrs.org/project/issues?id=org.openmrs%3Aopenmrs&issues=AWc_xKDcXGJ5mS2Bk7u_&open=AWc_xKDcXGJ5mS2Bk7u_

Solution:
In all cases merge collapsible "if" statements.